Quantum photonic imagers and methods of fabrication thereof

ABSTRACT

Emissive quantum photonic imagers comprised of a spatial array of digitally addressable multicolor pixels. Each pixel is a vertical stack of multiple semiconductor laser diodes, each of which can generate laser light of a different color. Within each multicolor pixel, the light generated from the stack of diodes is emitted perpendicular to the plane of the imager device via a plurality of vertical waveguides that are coupled to the optical confinement regions of each of the multiple laser diodes comprising the imager device. Each of the laser diodes comprising a single pixel is individually addressable, enabling each pixel to simultaneously emit any combination of the colors associated with the laser diodes at any required on/off duty cycle for each color. Each individual multicolor pixel can simultaneously emit the required colors and brightness values by controlling the on/off duty cycles of their respective laser diodes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/964,642 filed Dec. 26, 2007 which claims the benefit of U.S.Provisional Patent Application No. 60/975,772 filed Sep. 27, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to emissive imager devices comprising amonolithic semiconductor arrays of multicolor laser emitters that can beused as an image sources in digital projection systems.

2. Prior Art

The advent of digital display technology is causing a phenomenal demandfor digital displays. Several display technologies are poised to addressthis demand; including Plasma Display Panel (PDP), Liquid CrystalDisplay (LCD), and imager based projection displays that usemicro-mirrors, a liquid crystal on silicon (LCOS) device or a hightemperature poly-silicon (HTPS) device (Ref. [33]). Of particularinterest to the field of this invention are projection based displaysthat use imager devices, such as those mentioned, as an image formingdevice. These types of displays are facing strong competition from PDPand LCD displays and as such are in critical need for effective means toimprove their performance while significantly reducing their cost. Theprimary performance and cost driver in these types of displays are theimagers used, such as micro-mirrors, LCOS and HTPS devices. Beingpassive imagers, such devices require complex illumination optics andend up wasting a significant part of the generated light, which degradesthe performance and increases the cost of the display system. Theobjective of this invention is to overcome the drawbacks of such imagerdevices by introducing an emissive imager device which comprises anarray of multicolor laser emitters that can be used as an image sourcein digital projection systems.

FIGS. 1A and 1B are block diagram illustrations of typical projectorarchitectures 100 used in projection display systems that use a passiveimagers, such as those that use reflective imagers includingmicro-mirrors or LCOS imager devices (FIG. 1A) and those that use atransmissive imager, such as HTPS imager devices (FIG. 1B);respectively. In general, the projector 100 of a typical projectiondisplay system of FIG. 1A is comprised of an imager 110, illuminated bythe illumination optics 120 which couples the light generated by thelight source 130 onto the surface of the imager 120. The light source130 can either be a lamp that generates white light or a semiconductorlight source, such as light emitting diodes (LED) or laser diodes, thatcan generate Red (R), Green (G) or Blue (B) light.

In the case of the projector 100 that uses a reflective imagerillustrated in FIG. 1A, when a lamp is used as a light source, a colorwheel incorporating R, G and B filters is added between the illuminationoptics and the imager to modulate the required color. When asemiconductor light source is used in conjunction with a reflectiveimager, the color is modulated by turning on the semiconductor lightsource device having the required color, being either R, G or B.

In the case of a projector 100 that uses the transmissive imagerillustrated in FIG. 1B, when a lamp is used as a light source, theillumination optics 120 includes optical means for splitting thewhite-light generated by the lamp into R, G and B light patches thatilluminate the backsides of three HTPS imager devices and a dichroicprisms assembly is added to combine the modulated R, G and B light andcouple it on the projection optics 140.

The projection optics 140 is optically coupled to the surface of theimager 110 and the drive electronics 150 is electrically coupled to theimager 110. The optical engine generates the image to be projected bymodulating the intensity of the light generated by the light source 130,using imager 110, with the pixel grayscale input provided as image datato the drive electronics 150. When a reflective imager (FIG. 1A) such asmicro-mirror or LCOS imager device is used, the drive electronicsprovides the pixel grayscale data to the imager 110 and synchronizes itsoperation either with the sequential order of the R, G and B segments ofthe color wheel, when a white light lamp is used as a light source, orwith the sequential order in which the R, G or B semiconductor lightsource is turned on. When a transmissive imager such as the HTPS imagerdevice is used, the drive electronics provides the pixel grayscale datato the imager 110 and synchronizes the operation of each of the R, G andB HTPS imager devices in order to modulate the desired color intensityfor each pixel.

Typically the losses associated with the coupling of light onto thesurface of imager 110 are significant because they include the intrinsiclosses associated with the imager 110 itself, such as the devicereflectivity or the transmissivity values, plus the losses associatedwith collecting the light from the light source 130, collimating,filtering and relaying it to the surface of the imager 110. Collectivelythese losses can add up to nearly 90%; meaning that almost 90% of thelight generated by the light source 130 would be lost.

In addition, in the case of a reflective imager 110 such as micro-mirroror LCOS imager devices, the imager 110 being comprised of a spatialarray of reflective pixels, sequentially modulates the respective colorsof the light coupled onto its pixelated reflective surface by changingthe reflective on/off state of each individual pixel during the timeperiod when a specific color is illuminated. In effect, a typical priorart reflective imager can only modulate the intensity of the lightcoupled onto its pixelated reflective surface, a limitation which causesa great deal of inefficiency in utilizing the luminous flux generated bythe light source 130, introduces artifacts on the generated image, addscomplexities and cost to the overall display system and introduces yetanother source of inefficiency in utilizing the light generated by thelight source 130. Furthermore, both the reflective as well as thetransmissive type imagers suffer from an effect known as “photonicleakage” which causes light to leak onto the off-state pixels, whichsignificantly limits the contrast and black levels that can be achievedby these types of imagers.

As stated earlier, the objective of this invention is to overcome thedrawbacks of prior art imagers by introducing an emissive imager devicecomprising an array of multicolor laser emitters that can be used as animage source in digital projection systems. Although semiconductor laserdiodes have recently become an alternative light source 130 (Ref.[1]-[4]) for use in projectors 100 of FIG. 1A to illuminate reflectiveimagers 110 such as the micro-mirror imager device, the use ofsemiconductor laser diodes as a light source does not help in overcomingany of the drawbacks of prior art imagers discussed above. In additionnumerous prior art exists that describes projection displays that uses ascanned laser light beam to generate a projection pixel (Ref. [5]-[6]).

Prior art Ref. [7] describes a laser image projector comprising a twodimensional array of individually addressable laser pixels, each beingan organic vertical cavity laser pumped by an organic light emittingdiode (OLED). The pixel brightness of the laser image projectordescribed in prior art Ref. [7] would be a small fraction of thatprovided by the pumping light source, which, being an OLED based lightsource, would not likely to offer an ample amount of light, renderingthe brightness generated by the laser projector of prior art Ref. [7]hardly sufficient to be of practical use in most projection displayapplications.

Although there exist numerous prior art references that describe laserarrays (Ref. [8]-[30]), no prior art was found that teaches the use ofmulticolor laser emitters as pixels in an imager device. As it willbecome apparent in the following detailed description, this inventionrelates a separately addressable array of multicolor laser pixels formedby optically and electrically separating a monolithic layered stack oflaser emitting semiconductor structures. With regard to creating anoptically and electrically separated (isolated) semiconductor laseremitter array, Ref. [10] teaches methods for forming a single wavelengthlaser semiconductor structure with isolation regions (i.e. physicalbarriers) between the light emitting regions formed by either removingmaterial between the light emitting regions or by passivating theregions between the light emitters of the semiconductor structure.However, the methods described in Ref. [10] could only be used to createa one-dimensional linear array of separately addressable singlewavelength laser emitters within the range of wavelength from 700 to 800nm.

With regard to creating an array of separately addressable multicolorlaser emitters, Ref [21] describes an edge emitting array of red andblue laser structures. Although Ref. [21] deals with multicolor laserstructure, it is only related to a two-color one-dimensional lineararray of edge emitting laser structures.

Although Ref. [22] describes a display system that uses an array ofvertical cavity surface emitting laser (VCSEL) diodes, because of theinherent size of the VCSEL diodes described in Ref. [22], the approachdescribed would tend to produce substantially large pixels size becauseof the inherent size of the multiple color of VCSEL diodes it uses whichare arranged side-by-side in the same plane to form a pixel array,rendering it not usable as an imager device.

Given the aforementioned drawbacks of currently available imagerdevices, an imager that overcomes such weaknesses is certain to have asignificant commercial value. It is therefore the objective of thisinvention to provide an emissive imager device comprising a monolithicsemiconductor 2-dimensional array of multicolor laser emitters that canbe used as an image source in digital projection systems. Additionalobjectives and advantages of this invention will become apparent fromthe following detailed description of a preferred embodiments thereofthat proceeds with reference to the accompanying drawings.

REFERENCES

U.S. Patent Documents

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BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements.

FIGS. 1A and 1B illustrate the projection display architectural contextof the prior art imager imagers.

FIG. 2A illustrates an isometric view of the Quantum Photonic imagerdevice of this invention.

FIG. 2B illustrates an isometric view of the multicolor pixel comprisingthe emissive surface of the Quantum Photonic imager device of thisinvention.

FIG. 2C illustrates a top view of the Quantum Photonic imager device ofthis invention.

FIG. 2D illustrates an isometric view of an alternate Quantum Photonicimager device of this invention.

FIG. 3 illustrates a cross-sectional view of the multicolor pixel laserstack.

FIG. 4A illustrates a detailed cross-sectional view of the red laserdiode structure of the Quantum Photonic imager device of this invention.

FIG. 4B illustrates a detailed cross-sectional view of the green laserdiode structure of the Quantum Photonic imager device of this invention.

FIG. 4C illustrates a detailed cross-sectional view of the blue laserdiode structure of the Quantum Photonic imager device of this invention.

FIG. 4D illustrates a detailed cross-sectional view of an alternativered laser diode structure of the Quantum Photonic imager device of thisinvention.

FIG. 5A illustrates the energy band diagram of the red laser diodestructure of the Quantum Photonic imager device of this invention.

FIG. 5B illustrates the energy band diagram of the green laser diodestructure of the Quantum Photonic imager device of this invention.

FIG. 5C illustrates the energy band diagram of the blue laser diodestructure of the Quantum Photonic imager device of this invention.

FIG. 6A illustrates a horizontal cross-sectional view of the multicolorpixel sidewall.

FIG. 6B illustrates a vertical cross-sectional view of the multicolorpixel sidewall.

FIG. 6C illustrates the multicolor pixel sidewall contact vias layout.

FIG. 7 illustrates the multicolor pixel contact pad layout.

FIG. 8A illustrates a vertical cross-sectional view of the multicolorpixel output waveguide.

FIG. 8B illustrates a horizontal cross-sectional view of the multicolorpixel output waveguide.

FIG. 9A illustrates the intensity profile of the light emitted by themulticolor laser imager of this invention.

FIG. 9B illustrates the multiplicity of patterns in which the verticalwaveguides of the multicolor laser imager of this invention can bearranged.

FIG. 10A illustrates the a vertical cross-section of the digitalsemiconductor structure of the Quantum Photonic Imager device of thisinvention.

FIG. 10B illustrates the layout of contact metal layer interfacing thephotonic and digital semiconductor structures of the Quantum PhotonicImager device of this invention.

FIG. 10C illustrates the layout of the metal layers used for powersignals within the Quantum Photonic Imager device of this invention.

FIG. 10D illustrates the layout of the metal layers used for routingload and enable signals within the Quantum Photonic Imager device ofthis invention.

FIG. 10E illustrates the layout of the metal layers used for routingdata and control signals within the Quantum Photonic Imager device ofthis invention.

FIG. 11A illustrates the digital control logic of the Quantum PhotonicImager device of this invention.

FIG. 11B illustrates the digital logic cell associated with each of thepixels comprising the Quantum Photonic Imager device of this invention.

FIG. 12 illustrates a semiconductor process flow used to fabricate theQuantum Photonic imager device of this invention.

FIG. 13 illustrates a cross-sectional view of an exemplary projectorthat uses the Quantum Photonic imager device of this invention asdigital image source.

FIG. 14A illustrates the color gamut of the Quantum Photonic imagerdevice of this invention.

FIG. 14B illustrates the synthesize of exemplary pixels using theQuantum Photonic imager device of this invention.

FIG. 15A illustrates a block diagram of the image data processorcompanion device of the Quantum Photonic Imager device of thisinvention.

FIG. 15B illustrates the Quantum Photonic Imager device timing diagram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

References in the following detailed description of the presentinvention to “one embodiment” or “an embodiment” means that a particularfeature, structure, or characteristics described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of the phrase “in one embodiment” in various places in thisdetailed description are not necessarily all referring to the sameembodiment.

An emissive imager is described herein. In the following description,for the purpose of explanation, numerous specific details are set forthin order to provide a thorough understanding of the invention. It willbe apparent, however, to one skilled in the art that the invention canbe practiced with different specific details. In other instance,structures and devices are shown in block diagram form in order to avoidobscuring the invention.

QPI Architecture

The emissive multicolor digital image forming device described herein,referred to as “Quantum Photonic imager” (QPI), is a semiconductordevice comprising a monolithic array of multicolor laser emitters. TheQuantum Photonic imager of this invention is comprised of a plurality ofemissive multicolor pixels whereby in one embodiment, each pixelcomprises a stack of red (R), green (G) and blue (B) light emittinglaser diodes. The multicolor laser light of each said pixel is emittedperpendicular to the surface of the Quantum Photonic imager device via aplurality of vertical waveguides that are optically coupled to theoptical confinement region of each the R, G and B laser diodescomprising each pixel. The plurality of pixels that comprise the QuantumPhotonic imager devices are optically and electrically separated bysidewalls of insulating semiconductor material embedded in which are theelectrical interconnects (vias) that are used to route electricalcurrent to the constituent laser diodes of each pixel. Each of theplurality of pixels that comprise the Quantum Photonic imager devices iselectrically coupled to a control logic circuit that routes (enable) theelectric current signal to each of its constituent red (R), green (G)and blue (B) laser diodes. The drive logic circuits associated with theplurality of pixels form a drive logic array that is bonded togetherwith the stack of red (R), green (G) and blue (B) laser diodes to form amonolithic array of multicolor laser pixels and drive circuitry.

FIGS. 2A, 2B and 2C illustrate a preferred embodiment of the QuantumPhotonic Imager device 200 of this invention. FIG. 2A illustrates anisometric view of the Quantum Photonic imager device 200, while FIG. 2Billustrates and isometric view of one of its constituent pixels 230 andFIG. 2C is a top view illustration that shows the array of pixels 230comprising the Quantum Photonic imager device 200 and the digitalcontrol logic 229 positioned at the periphery of the pixel array.

As illustrated in FIG. 2A, the Quantum Photonic imager device 200 wouldbe comprised of two semiconductor structures; namely the photonicsemiconductor structure 210 and the digital semiconductor structure 220.The semiconductor structures 210 and 220 are bonded together eitherthrough die-level bonding or wafer-level bonding to form the QuantumPhotonic imager device 200 illustrated in FIG. 2A. Each of the twosemiconductor structures comprising the Quantum Photonic imager device200 is further comprised of multiple semiconductor layers. Asillustrated in FIG. 2A, the digital semiconductor structure 220 of theQuantum Photonic imager device 200 would typically be larger in surfacearea than the photonic semiconductor structure 210 to allow for theplacement of the digital control logic 229 and the bonding pads 221,through which the power and image data signals are provided to thedevice, to be accessible at the topside of the device. The photonicsemiconductor structure 210 is comprised of a plurality of emissivemulticolor pixels and digital semiconductor structure 220 is comprisedof the digital drive logic circuits that provide power and controlsignals to the photonic semiconductor structure 210.

FIG. 2B is a cutaway isometric illustration of the semiconductorstructure of one of the pixels 230 comprising the Quantum Photonicimager device 200 of one embodiment of this invention. As illustrated inFIG. 2B, each of the pixels 230 would have a sidewall 235 that providesoptical and electrical separation between adjacent pixels. As will beexplained in more detail in subsequent paragraphs, the electricalinterconnects required to supply power signals to the photonicsemiconductor structure 210 portion of the pixels 230 would be embeddedwithin the pixel sidewalls 235.

As illustrated in the pixel isometric cutaway view of FIG. 2B, theportion of the photonic semiconductor structure 210 within the interiorof the pixels 230 would be comprised of the semiconductor substrate 240,a red (R) laser diode multilayer 231, a green (G) laser diode multilayer232 and a blue (B) laser diode multilayer 233 stacked vertically. Thelaser light of each of the pixels 230 comprising the Quantum Photonicimager device 200 would be emitted in a direction that is perpendicularto the plane of the device top surface, hereinafter referred to as thevertical direction, through the plurality of vertical waveguides 290,each of which is optically coupled to the optical resonator (or theoptical confinement region) of each of the laser diodes 231, 232 and233. The plurality of vertical waveguides 290 would form a laser emitterarray that would define the laser light emission cross section (oroptical characteristics) of each of the pixels 230 comprising theQuantum Photonic imager device 200 of this invention. The novel approachof this invention of vertically stacking the laser diodes 231, 232 and233 and optically coupling the vertical waveguides 290 to the opticalresonator (or the optical confinement region) of each of the stackedlaser diodes 231, 232 and 233 would enable multicolor laser lightgenerated by these laser diodes to be emitted through the array ofvertical waveguides 290, thus making the pixels 230 comprising theQuantum Photonic imager device 200 of this invention become emissivemulticolor laser pixels.

FIG. 2C is a top view illustration of the Quantum Photonic imager device200 showing the top of the photonic semiconductor structure 210comprising the 2-dimensional array of multicolor pixels 230 that formsthe emissive surface of the device and the top of the digitalsemiconductor structure 220 extending beyond that of the photonicsemiconductor structure 210 to allow for the area required for thedevice bonding pads 221 and the layout area for the device control logic229. The typical size of the pixels 230 of the preferred embodiment ofthe Quantum Photonic Imager 200 of this invention would be in the rangeof 10×10 micron, making the emissive surface of a Quantum Photonicimager device 200 that provides a VGA resolution (640×480 pixels) be6.4×4.8 mm. The actual size of the photonic semiconductor structure 210would extend beyond emissive surface area by few additional pixels oneach side, making the typical size of the photonic semiconductorstructure 210 be in the range of 6.6×5 mm and the digital semiconductorstructure 220 would extend beyond that area to allow for the layout areaof the control logic 229 and the device bonding pads 221, making thetypical dimensions of a Quantum Photonic imager device 200 that providesa VGA resolution be in the range 7.6×6 mm.

Having described the underlying architecture of the Quantum PhotonicImager devices 200 of this invention, the following paragraphs providedetailed description of its constituent parts and manufacturing methodsthereof.

QPI Semiconductor Structure

FIG. 3 is a cross-sectional view illustration of the semiconductor multistructures that form the Quantum Photonic Imager Device 200 of thisInvention. The same reference numbers are used for the same items,however the red, green and blue laser diodes semiconductor structuresprior to the formation of the pixels 230 would be referred to as themultilayer laser diode structures 250, 260 and 270; respectively.

In accordance with the preferred embodiment of the fabrication method ofthe Quantum Photonic Imager device 200 of this invention, the multilayerlaser diode structures 250, 260 and 270 would be fabricated separatelyas semiconductor wafers using the appropriate semiconductor processes,then post-processed to create the wafer-size multilayer stack photonicsemiconductor structure 210 that incorporates the metal and insulationlayers as illustrated in FIG. 3. The wafer-size multilayer stackphotonic semiconductor structure 210 would then be furtherpost-processed to create the pixels' sidewalls 235, which form the laserdiodes 231, 232 and 233, and the pixels' vertical waveguide 290 asillustrated in FIG. 2B. Furthermore, the digital semiconductor structure220 would also be fabricated separately as a semiconductor wafer usingthe appropriate semiconductor processes, then wafer-level or die-levelbonded with the multilayer stack photonic semiconductor structure 210 tocreate the Quantum Photonic Imager device 200 illustrated in FIG. 2A.The following paragraphs describe the detailed design specifications ofthe multilayer laser diode structures 250, 260 and 270 and the digitalsemiconductor structure 220 as well as the detailed designspecifications of the wafers post-processing and fabrication flowrequired to create the Quantum Photonic Imager device 200 of thisinvention.

The illustration of FIG. 3 shows the Quantum Photonic Imager device 200being comprised of the semiconductor structures 210 and 220 with each ofthese two semiconductor structures being further comprised of multiplesemiconductor layers. As illustrated in FIG. 3, the photonicsemiconductor structure 210 is comprised of a silicon (Si) substrate 240and a stack of three multilayer laser diode structures 250, 260 and 270separated by layers 241, 251, 261 and 271 of dielectric insulator, suchas silicon dioxide (SiO₂), each preferably 150 to 200 nm-thick, whichprovide top and bottom electrical insulation of each between the threemultilayer laser diode structures 250, 260 and 270.

Also incorporated within the photonic semiconductor structure 210 arethe metal layers 252 and 253, which constitute the p-contact andn-contact metal layers; respectively, of the red multilayer laser diode250, the metal layers 262 and 263 which constitute the p-contact andn-contact metal layers; respectively, of the green multilayer laserdiode 260 and the metal layers 272 and 273 which constitute thep-contact and n-contact metal layers; respectively, of the bluemultilayer laser diode 270. Each of the metal layers 252, 253, 262, 263,272 and 273 is preferably 150 to 200 nm-thick of semiconductorinterconnect metallization layer having low electromigration andstress-migration characteristics such as gold-tin (Au—Sn) orgold-titanium (Au—Ti) multilayer metallization. The metallization layers252, 253, 262, 263, 272 and 273 would also include a diffusion barrierthat would prevent excessive diffusion of the metallization layers intothe insulation layers 241, 252, 261 and 271.

As illustrated in FIG. 3, the interfaces between the semiconductorstructures 210 and 220 are the metal layer 282, at the photonicsemiconductor structure 210 side, and the metal layer 222 at the digitalcontrol structure 220 side. Both of the metal layers 282 and 222 wouldbe etched to incorporate the electrical interconnect bonding padsbetween the two semiconductor structures 210 and 220. The metal layer222 would also incorporate the device bonding pads 221.

The insulation layers 241, 251, 261 and 271 and metallization layers252, 253, 262, 263, 272 and 273 would be deposited using typicalsemiconductor vapor deposition process such as chemical vapor deposition(CVD). The two layers 241 and 252 would be deposited directly on the Sisubstrate layer 240, and the resultant multilayer stack 240-241-252 isthen wafer-level bonded to the p-layer of the red laser diode structure250 using either direct wafer bonding, diffusion bonding or anodicbonding techniques or the like.

The resultant semiconductor multilayer structure is then used as asubstrate upon which the layers 253, 251, and 262 would be depositedusing vapor deposition techniques such as CVD or the like and theresultant multilayer stack 240-241-252-250-253-251-262 is thenwafer-level bonded to the p-layer of the green laser diode structures260 using either direct wafer bonding, diffusion bonding or anodicbonding techniques or the like, and the substrate on which the greenlaser diode was formed is removed.

The resultant semiconductor multilayer structure is then used as asubstrate upon which the layers 263, 261, and 272 would be depositedusing vapor deposition techniques such as CVD or the like and theresultant multilayer stack 240-241-252-250-253-251-262-260-263-261-272is then wafer-level bonded to the p-layer of the blue laser diodestructures 270 using either direct wafer bonding, diffusion bondinganodic bonding techniques or the like, and the substrate on which theblue laser diode was formed is removed.

The resultant semiconductor multilayer structure is then used as asubstrate upon which the layers 273, 271, and 282 would be depositedusing vapor deposition techniques such as CVD or the like. The metallayer 282 is then etched to create the bonding pad pattern usingsemiconductor lithography process and the etched areas are refilled withinsulator material, preferably SiO₂, and the surface is then polishedand cleaned. The resultant photonic semiconductor structure 210 is thenwafer-level bonded to the corresponding bonding pad surface of thedigital semiconductor structure 220 using flip-chip bonding techniques.

Laser Diode Multilayer Structure

Each of the multilayer semiconductor structures 250, 260 and 270 wouldbe a multiple quantum well (MQW) double heterostructure semiconductorlaser diode grown as separate wafers each on its own substrate usingwell-known epitaxial deposition process commonly referred to asmetal-organic chemical vapor deposition (MOCVD). Other depositionprocesses such as liquid phase epitaxy (LPE), molecular beam epitaxy(MBE), metal organic vapor phase epitaxy (MOVPE), hydride vapor phaseepitaxy (HVPE), hydride metal organic vapor phase epitaxy (H-MOVPE) orother known crystal growth processes can also be used.

Red Laser Diode

FIG. 4A illustrates an exemplary embodiment of the multilayer crosssection of the red laser diode structure 250 of the Quantum Photonicimager device 200 of this invention. The multilayer semiconductorstructure of FIG. 4A is phosphide based with its parameters selectedsuch that the laser light generated by the red laser diode structure 250would have a dominant wavelength of 615-nm. As shown in FIG. 4A, asubstrate removal etch-stop layer 412 of n-doped GaAs of thickness100-nm is grown on a thick (approximately 2000 nm) GaAs substrate 410which will be etched off after the red laser diode structure 250 iswafer-level bonded to the multilayer stack 240-241-252 as explainedearlier. The n-doped GaAs etch-stop layer 412 would have either silicon(Si) or selenium (Se) doping of approximately 8×10¹⁸ cm⁻³. A thick GaAssubstrate is used to assure the growth of a high quality epi layerthereon.

Upon the substrate removal etch-stop layer 412 is deposited the claddinglayer 414 of n-type of either Al_(0.5)In_(0.5)P or(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5) superlattice (SL) which would typicallybe 120-nm thick and have either Si or Se doping of 1×10¹⁸ cm⁻³. Upon thecladding layer 414 is deposited a 100-nm thick n-type(Al_(0.55)Ga_(0.45))_(0.5)In_(0.5)P waveguide layer 416 which wouldtypically be either silicon (Si) or selenium (Se) doped to at least1×10¹⁸ cm⁻³. Upon the waveguide layer 416 is deposited the active region421 of the red laser diode 250 comprised of multiple Ga_(0.6)In_(0.4)Pquantum well layers 420 which are enclosed within the Al_(0.5)In_(0.5)Pbarrier layers 418, typically either silicon (Si) or selenium (Se) dopedat levels of least 0.01×10¹⁸ cm⁻³ and 0.1×10¹⁸ cm⁻³, respectively. Asshown in FIG. 4A, the thickness of the quantum well layers 420 andbarrier layers 418 are selected to be 4.8-nm and 4-nm; respectively,however the thickness of these layers could be increased or decreased inorder to fine tune the emission characteristics of the red laser diode250.

Although FIG. 4A shows the active region 421 of the red laser diode 250being comprised of three quantum wells, the number of quantum wells usedcould be increased or decreased in order to fine tune the emissioncharacteristics of the red laser diode 250. Furthermore, the activeregion 421 of the red laser diode 250 could also be comprised ofmultiplicity of quantum wires or quantum dots instead of quantum wells.

Above the active region 421 is deposited a 140-nm thick p-type(Al_(0.55)Ga_(0.45))_(0.5)In_(0.5)P waveguide layer 422 which wouldtypically be magnesium (Mg) doped at a level of at least 1×10¹⁸ cm⁻³.Upon waveguide layer 422 is deposited a 23-nm thick Al_(0.5)In_(0.5)Panti-tunneling layer 424 having a magnesium doping level of at least1×10¹⁸ cm⁻³. Upon anti-tunneling layer 424 is deposited an electronblocker layer 426 of thickness 25-nm which is comprised alternatinglayers of Ga_(0.5)In_(0.5)P quantum wells and Al_(0.5)In_(0.5)P barrierseach being magnesium doped at a level of at least 1×10¹⁸ cm⁻³. Theelectron blocker layer 426 is incorporated in order to reduce theelectron leakage current, which would reduce the threshold current andthe operating temperature of the red laser diode structure 250.

Above the electron blocker layer 426 is deposited a 120-nm thick p-typeof either Al_(0.5)In_(0.5)P or (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5) SLcladding layer 428 which would typically be magnesium doped at a levelof 0.5×10¹⁸ cm⁻³. Upon the cladding layer 428 is deposited a 100-nmthick p-type GaAs contact layer 429 which would heavily magnesium dopedat a level of at least 1×10¹⁸ cm⁻³. As explained earlier, the contactlayer 429 would be the interface layer for the wafer-level bonding ofthe red laser diode structure 250 and the multilayer stack 240-241-252.

The multilayer 416-421-422 is known to a person skilled in the art asthe optical resonator or optical confinement region of the red laserdiode 250 within which the red laser light generated by the MQW activeregion 421 would be confined. As will be explained in the subsequentparagraphs, the light generated by the red laser diode 250 will beemitted vertically from the surface of the Quantum Photonic imagerdevice 200 through vertical waveguides 290 that are optically coupled tothe optical confinement multilayer 416-421-422 of the red laser diode250.

Green Laser Diode

FIG. 4B illustrates an exemplary embodiment of the multilayer crosssection of the green laser diode structure 260 of the Quantum Photonicimager device 200 of this invention. The multilayer semiconductorstructure of FIG. 4B is nitride based with its parameters are selectedsuch that the laser light generated by the green laser diode structure260 would have a dominant wavelength of 520-nm. As shown in FIG. 4B, asubstrate removal etch-stop layer 432 of n-doped In_(0.05)Ga_(0.95)N ofthickness 100-nm and Si-doped at a level 6×10¹⁸ cm⁻³ is grown on a thickGaN substrate 430 which will be etched off after the green laser diodestructure 260 is wafer-level bonded to the multilayer stack240-241-252-250-53-251-262 as explained earlier. The n-dopedIn_(0.05)Ga_(0.95)N etch-stop layer 432 would have silicon (Si) dopingof 6×10¹⁸ cm⁻³. Although FIG. 4B shows the substrate 430 being GaN,InGaN material alloy could also be used for the substrate 430.

Upon the substrate removal etch-stop layer 432 is deposited the claddinglayer 434 of n-type of Al_(0.18)Ga_(0.82)N/GaN SL which would typicallybe 451-nm thick and have Si doping of 2×10¹⁸ cm⁻³. Upon the claddinglayer 434 is deposited a 98.5-nm thick n-type GaN waveguide layer 436which would typically be Si-doped at a level of 6.5×10¹⁸ cm⁻³. Upon thewaveguide layer 436 is deposited the active region of the green laserdiode 260 which is comprised of multiple In_(0.535)Ga_(0.465)N quantumwell layers 450 each being Si-doped at a level of 0.05×10¹⁸ cm⁻³ andenclosed within the In_(0.04)Ga_(0.96)N barrier layers 438 each beingSi-doped at a level of 6.5×10¹⁸ cm⁻³. As shown in FIG. 4B, the thicknessof the quantum well layers 450 and barrier layers 438 are selected to be5.5-nm and 8.5-nm; respectively, however the thickness of these layerscould be increased or decreased in order to fine tune the emissioncharacteristics of the green laser diode 260.

Although FIG. 4B shows the active region 431 of the green laser diode260 being comprised of three quantum wells, the number of quantum wellsused could be increased or decreased to in order to fine tune theemission characteristics of the green laser diode 260. Furthermore, theactive region 431 of the green laser diode 260 could also be comprisedof multiplicity of quantum wires or quantum dots instead of quantumwells.

Above the active region 431 is deposited a 8.5-nm thick p-type GaNwaveguide layer 452 which would typically be magnesium (Mg) doped at alevel of 50×10¹⁸ cm⁻³. Upon waveguide layer 452 is deposited a 20-nmthick Al_(0.2)Ga_(0.8)N electron blocker layer 454 having a magnesium(Mg) doping level of approximately 100×10¹⁸ cm⁻³. The electron blockerlayer 454 is incorporated in order to reduce the electron leakagecurrent, which would reduce the threshold current and the operatingtemperature of the green laser diode structure 260.

Above the electron blocker layer 454 is deposited a 90-nm thick p-typeGaN waveguide layer 456 which would typically be magnesium (Mg) doped ata level of 75×10¹⁸ cm⁻³. Upon the waveguide layer 456 is deposited a451-nm thick p-type Al_(0.18)Ga_(0.82)N/GaN SL cladding layer 458 whichwould typically be magnesium doped at a level of 75×10¹⁸ cm⁻³. Upon thecladding layer 458 is deposited a 100-nm thick p-type GaN contact layer459 which is magnesium (Mg) doped at a level of 75×10¹⁸ cm⁻³. Asexplained earlier, the contact layer 459 would be the interface layerfor the wafer-level bonding of the green laser diode structure 260 andthe multilayer stack 240-241-252-253-251-262.

The multilayer 436-431-452 is known to a person skilled in the art asthe optical resonator or optical confinement region of the green laserdiode 260 within which the green laser light generated by the MQW activeregion 431 would be confined. As will be explained in the subsequentparagraphs, the light generated by the green laser diode 260 will beemitted vertically from the surface of the Quantum Photonic imagerdevice 200 through vertical waveguides 290 that are optically coupled tothe optical confinement multilayer 436-431-452 of the green laser diode260.

Blue Laser Diode

FIG. 4C illustrates an exemplary embodiment of the multilayer crosssection of the blue laser diode structure 260 of the Quantum Photonicimager device 200 of this invention. The multilayer semiconductorstructure of FIG. 4C is nitride based with its parameters selected suchthat the laser light generated by the blue laser diode structure 260would have a dominant wavelength of 460-nm. As shown in FIG. 4C, asubstrate removal etch-stop layer 462 of n-doped In_(0.05)Ga_(0.95)N ofthickness 100-nm Si doped at a level 6×10¹⁸ cm⁻³ is grown on a thick GaNsubstrate 460 which will be etched off after the blue laser diodestructure 270 is wafer-level bonded to the multilayer stack240-241-252-250-53-251-262-260-263-261-272 as explained earlier. Then-doped In_(0.05)Ga_(0.95)N etch-stop layer 462 would have silicon (Si)doping of 6×10¹⁸ cm⁻³. Although FIG. 4C shows the substrate 460 beingGaN, InGaN material alloy could also be used for the substrate 460.

Upon the substrate removal etch-stop layer 462 is deposited the claddinglayer 464 of n-type of Al_(0.18)Ga_(0.82)N/GaN SL which would typicallybe 451-nm thick and have Si doping of 2×10¹⁸ cm⁻³. Upon the claddinglayer 464 is deposited a 98.5-nm thick n-type GaN waveguide layer 466which would typically be Si doped at a level of 6.5×10¹⁸ cm⁻³. Upon thewaveguide layer 466 is deposited the active region of the blue laserdiode 270 which is comprised of multiple In_(0.41)Ga_(0.59)N quantumwell layers 470 each being Si-doped at a level of 0.05×10¹⁸ cm⁻³ andenclosed within the In_(0.04)Ga_(0.96)N barrier layers 468 each beingSi-doped at a level of 6.5×10¹⁸ cm⁻³. As shown in FIG. 4C, the thicknessof the quantum well layers 470 and barrier layers 468 are selected to be5.5-nm and 8.5-nm; respectively, however the thickness of these layerscould be increased or decreased in order to fine tune the emissioncharacteristics of the blue laser diode 270.

Although FIG. 4C shows the active region 431 of the green laser diode260 being comprised of three quantum wells, the number of quantum wellsused could be increased or decreased in order to fine tune the emissioncharacteristics of the green laser diode 260. Furthermore, the activeregion 431 of the blue laser diode 260 could also be comprised ofmultiplicity of quantum wires or quantum dots instead of quantum wells.

Above the active region 431 is deposited a 8.5-nm thick p-type GaNwaveguide layer 472 which would typically be magnesium (Mg) doped at alevel of 50×10¹⁸ cm⁻³. Upon waveguide layer 472 is deposited a 20-nmthick Al_(0.2)Ga_(0.8)N electron blocker layer 474 having a magnesium(Mg) doping level of approximately 100×10¹⁸ cm⁻³. The electron blockerlayer 474 is incorporated in order to reduce the electron leakagecurrent, which would reduce the threshold current and the operatingtemperature of the blue laser diode structure 270.

Above the electron blocker layer 474 is deposited a 90-nm thick p-typeGaN waveguide layer 476 which would typically be magnesium (Mg) doped ata level of 75×10¹⁸ cm⁻³. Upon the waveguide layer 476 is deposited a451-nm thick p-type Al_(0.18)Ga_(0.82)N/GaN SL cladding layer 478 whichwould typically be magnesium (Mg) doped at a level of 75×10¹⁸ cm⁻³.

Upon the cladding layer 478 is deposited a 100-nm thick p-type GaNcontact layer 479 which is magnesium doped at a level of 75×10¹⁸ cm⁻³.As explained earlier, the contact layer 479 would be the layer for thewafer-level bonding of the blue laser diode structure 270 and themultilayer stack 240-241-252-253-251-262-260-263-261-272.

The multilayer 466-461-472 is known to a person skilled in the art asthe optical resonator or optical confinement region of the blue laserdiode 270 within which the blue laser light generated by the MQW activeregion 461 would be confined. As will be explained in the subsequentparagraphs, the light generated by the blue laser diode 270 will beemitted vertically from the surface of the Quantum Photonic imagerdevice 200 through vertical waveguides 290 that are optically coupled tothe optical confinement multilayer 466-461-472 of the blue laser diode270.

An alternative exemplary embodiment of the multilayer red laser diodestructure 250 of the Quantum Photonic imager device 200 that isnitride-based is illustrated in FIG. 4D. Being nitride-based, thealternative exemplary embodiment of the multilayer red laser diodestructure 250 of FIG. 4D would have comparable design prescription asthe nitride-based green laser diode structure 260 of FIG. 4B and theblue laser diode structure 270 of FIG. 4C, with the exception that itslayer parameters would be selected such that the generated laser lightwould have a dominant wavelength of 615-nm. The alternativenitride-based multilayer red laser diode structure 250 of FIG. 4D wouldbe enabled by the increase in the indium content of the multiple quantumwells 419 to 0.68. Although FIG. 4D shows its active region beingcomprised of three quantum wells, the number of quantum wells used couldbe increased or decreased in order to fine tune the emissioncharacteristics of the red laser diode 250. Furthermore, the activeregion of the alternative exemplary embodiment of the red laser diodestructure 250 illustrated in FIG. 4D could also be comprised ofmultiplicity of quantum wires or quantum dots instead of quantum wells.Although FIG. 4D shows the substrate 480 being GaN, InGaN material alloycould also be used for the substrate 480.

QPI Color Gamut

As will be subsequently explained, the color gamut defined by the threecolors specified for the laser diodes 250, 260 and 270 in theaforementioned exemplary embodiment of the Quantum Photonic Imagerdevice 200 would achieve an extended gamut (Wide Gamut) relative to thedefined standards of color image displays such HDTV and NTSC.Specifically, the three colors specified for the laser diodes 250, 260and 270 in the aforementioned exemplary embodiment of the QuantumPhotonic Imager device 200 would achieve a color gamut that is nearly200% of the color gamut defined by the NTSC standard.

The color gamut achieved by the Quantum Photonic Imager device 200 ofthis invention can be further extended to include more than 90% of thevisible color gamut to achieve an Ultra-Wide Gamut capability byincreasing the number of laser diodes incorporated within the photonicsemiconductor structure 210 beyond the three colors specified for thelaser diodes 250, 260 and 270 in the aforementioned exemplaryembodiment. Specifically the color gamut of the light emitted by theQuantum Photonic Imager device 200 could be extended further to achievean Ultra-Wide Gamut when the number of stacked laser diodes comprisingthe Quantum Photonic Imager device 200 is increased to include yellow(572-nm) laser diode semiconductor structure positioned in between thered and the green laser diodes structure 250 and 260 and a cyan (488-nm)laser diode semiconductor structure positioned in between the greenlaser diode structure 260 and the blue laser diode structure 270, thusmaking the Quantum Photonic Imager device 200 be comprised of a stack offive laser diode structures covering the wavelengths of red (615-nm),yellow (572-nm), green (520-nm), cyan (488-nm) and blue (460-nm). Withthis stack of five laser diode semiconductor structures 210 of theQuantum Photonic Imager device 200 of this invention would be able togenerate an Ultra-Wide color gamut that covers more than 90% of thevisible color gamut.

Although in the aforementioned exemplary embodiments of the photonicsemiconductor structure 210 of the Quantum Photonic Imager device 200,the wavelengths of the laser diode structures 250, 260, and 270 wereselected to be 615-nm, 520-nm and 460-nm; respectively, a person skilledin the art would know how to follow the teachings of this inventionusing other values of wavelengths than those selected for the laserdiode structures 250, 260, and 270 of the aforementioned exemplaryembodiments. Furthermore, although in the aforementioned exemplaryembodiments of the Quantum Photonic Imager device 200, the photonicsemiconductor structure 210 is comprised of the three laser diodestructures 250, 260, and 270, a person skilled in the art would know howto follow the teachings of this invention using more than three laserdiode structures. Furthermore, although in the aforementioned exemplaryembodiments of the Quantum Photonic Imager device 200, the photonicsemiconductor structure 210 is comprised of the three laser diodestructures 250, 260, and 270 stacked in the order illustrated in FIG. 3,a person skilled in the art would know how to follow the teachings ofthis invention with the laser diode structures stacked in a differentorder.

Laser Diodes Energy Bands

FIG. 5A, FIG. 5B and FIG. 5C illustrate the energy bands of theaforementioned exemplary embodiments of the phosphide based red laserdiode structure 250 and the nitride based green laser diode 260 and bluelaser diode 270; respectively. The energy bands shown in FIG. 5A, FIG.5B and FIG. 5C illustrate the thickness of each layer from left to rightand the energy from bottom to top. The thickness and energy levels aremeant to show qualitative values rather than a quantitative measure ofthe exact thicknesses and energy levels. Nevertheless, the referencenumbers in FIG. 5A, FIG. 5B and FIG. 5C correspond with the referencenumbers of the layers in FIG. 4A, FIG. 4B and FIG. 4C; respectively. Asthese figures illustrate, the energy levels of the p-type and n-typecladding layers energetically confine the p-type and n-type waveguidelayers as well as the multiple quantum well levels. Because the energylevels of the multiple quantum wells represent a local low energy level,as illustrated in figures FIG. 5A, FIG. 5B and FIG. 5C, electrons willbe confined within the quantum wells to be efficiently recombined withthe corresponding holes to generate light.

In reference to FIG. 5A, the thickness of the anti-tunneling layer 424is selected such that it is large enough to prevent electrons tunnelingyet small enough to retain electron coherence within the superlatticestructure of the electron blocker layer 426. In order to lower thelasing threshold, the electron blocker layers 426, 454 and 474 are usedin the exemplary embodiments of the laser diode structure 250, 260, and270; respectively. As illustrated in FIG. 5A, the electron blocker 426used in the red laser structure 250 is comprised of multiple quantumbarriers (MQB) implemented in the p-doped region and having energy levelalternating between that of the waveguide layer 422 and the claddinglayer 428. The inclusion of the MQB electron blocker 426 substantiallyimproves the electron confinement due to the quantum interference of theelectrons in the MQB, creating a large increase of the barrier height atthe waveguide-cladding layers interface, which substantially suppressesthe electron leakage current. As illustrated in FIG. 5B and FIG. 5C, theelectron blocker used in the green laser structure 260 and the bluelaser structure 270 is placed in between two segments of the p-typewaveguide layers and has energy level that is substantially higher thanboth the waveguide layers as well as the cladding layers in order tosubstantially improve the electron confinement and subsequentlysuppresses the electron leakage current.

Pixel Sidewalls

The plurality of pixels 230 that comprises the Quantum Photonic imagerdevice 200 are optically and electrically separated by the pixelsidewalls 235 comprised of insulating semiconductor material andembedded within which are the vertical electrical interconnects (contactvias) that are used to route electrical current to the constituent laserdiodes of each pixel. FIG. 6A is a horizontal cross sectional view ofone of the plurality multicolor pixels 230 comprising the QuantumPhotonic Imager device 200 that illustrates the inner structure of thepixel sidewall 235. As illustrated in FIG. 6A, the pixel sidewall 235defines the boundaries of the multicolor pixel 230 and is comprised ofthe metal contact vias 236 embedded within a sidewall interior 237 ofdielectric material such as SiO₂.

FIG. 6B is a vertical cross-sectional view of one of the pixel sidewalls235 that illustrates the interface between the multilayer photonicstructure 210 and the sidewall 235. The pixel sidewalls 235 illustratedin FIG. 6A and FIG. 6B would be formed by etching an orthogonal squaregrid of 1-micron wide trenches into the multilayer photonic structure210. The trenches would be etched at a pitch that equals the pixelwidth, which in this exemplary embodiment of the Quantum Photonic Imagerdevice 200 is selected to be 10-micron, and at a depth starting from thebonding pad layer 282 and ending at the SiO₂ insulation layer 241. Theetched trenches are then refilled with low dielectric constant (low-k)insulating material such as SiO₂ or silicon carbon-doped silicon oxide(SiOC) then re-etched to form 150-nm wide trenches for the contact vias236. The re-etched trenches for the contact vias 236 are then refilledusing vapor deposition techniques, such as CVD or the like, with metalsuch as gold-tin (Au—Sn) or gold-titanium (Au—Ti) to achieve contactwith the metallization layers 252, 253, 262, 263, 272 and 273.

The trenches etched for the pixel sidewalls 235 may have parallel sidesas illustrated in FIG. 6B or the may be slightly sloped as dictated bythe etching process used. Although any appropriate semiconductor etchingtechnique may be used for etching the trenches for the sidewalls 235 andthe contact via 236, one exemplary etching technique is a dry etchingtechnique, such as chlorine-based, chemically-assisted ion beam etching(Cl-based CAIBE). However, other etching techniques, such as reactiveion etching (RIE) or the like may be used.

The formation of the pixel sidewalls 235 as described above is performedin multiple intermediate stages during the formation of the multilayerphotonic structure 210. FIG. 6C is a vertical cross-sectional view ofthe contact vias 236 embedded within the pixel sidewalls 235. Asillustrated in FIG. 6C, each of the contact vias 236 would be comprisedof the six segments 254 and 256 for the red laser diode structure 250p-contact and n-contact; respectively, 264 and 266 for the green laserdiode structure 260 p-contact and n-contact; respectively, and 274 and276 for the blue laser diode laser 270 p-contact and n-contact;respectively.

After the multilayer structure 240-241-252-250 is formed as explainedearlier, the trench for the pixel sidewall 235 is double-etched into themultilayer structure from the side of the red laser diode multilayer 250with the first and second stop-etch being below and above the metallayer 252. The etched trench is then refilled with insulating materialsuch as SiO₂ then retched with the stop-etch being the metal layer 252and refilled with contact metal material to form the base segment of thecontact via 254 as illustrated in FIG. 6C.

After the contact layer 253 and the insulation layer 251 are deposited,the trench for the pixel sidewall 235 is double-etched into thedeposited layers with the first and second stop etch being below andabove the metal layer 253, refilled with insulating material, re-etchedwith the stop-etch being the metal layer 253 and refilled with contactmetal material to form the base of the contact via 256 and to extend thecontact via 254 as illustrated in FIG. 6C.

After the contact layer 262 is deposited and the green laser diodestructure 260 is bonded with the multilayer structure, the trench forthe pixel sidewall 235 is double-etched into the formed multilayerstructure from the side of the green laser diode multilayer 250 with thefirst and second stop-etch being below and above the metal layer 262.The etched trench is then refilled with insulating material such as SiO₂then retched with the stop-etch being the metal layer 262 and refilledwith contact metal material to form the base segment of the contact via264 and extend the contact vias 254 and 256 as illustrated in FIG. 6C.

After the contact layer 263 and the insulation layer 261 are deposited,the trench for the pixel sidewall 235 is double-etched into thedeposited layers with the first and second stop-etch being below andabove the metal layer 263, refilled with insulating material, re-etchedwith the stop-etch being the metal layer 263 and refilled with contactmetal material to form the base segment of the contact via 266 and toextend the contact vias 254, 256 and 264 as illustrated in FIG. 6C.

After the contact layer 272 is deposited and the blue laser diodestructure 270 is bonded with the multilayer structure, the trench forthe pixel sidewall 235 is double-etched into the formed multilayerstructure from the side of the green laser diode multilayer 250 with thefirst and second stop-etch being below and above the metal layer 272.The etched trench is then refilled with insulating material such as SiO₂then retched with the stop-etch being the metal layer 272 and refilledwith contact metal material to form the base segment of the contact via274 and extend the contact vias 254, 256, 264, and 266 as illustrated inFIG. 6C.

After the contact layer 273 and the insulation layer 271 are deposited,the trench for the pixel sidewall 235 is double-etched into thedeposited layers with the first and second stop-etch being below andabove the metal layer 273, refilled with insulating material, re-etchedwith the stop-etch being the metal layer 263 and refilled with contactmetal material to form the base segment of the contact via 276 and toextend the contact vias 254, 256, 264, 266 and 274 as illustrated inFIG. 6C.

After the pixel sidewalls 235 are formed, the metal layer 282 would bedeposited then etched to create separation trenches between metalcontacts established with contact vias 254, 256, 264, 266, 274 and 276and the etched trenches are then refilled with insulating material suchas SiO₂ then polished to create the pixel contact pad 700 which isillustrated in FIG. 7. The pixel contact pad 700 would form the contactinterface between the photonic semiconductor structure 210 and thedigital semiconductor structure 220.

Vertical Waveguides

After the formation of the pixel sidewalls 235 as explained above, thephotonic semiconductor structure 210 would be partitioned by the formedsidewalls 235 into electrically and optically separated square regionsthat define the individual pixels 230 of the photonic semiconductorstructure. The formed photonic semiconductor structure of each of thepixels 230 would then be comprised of a portion of the laser diodesemiconductor structures 250, 260 and 270 and will be designated 231,232 and 233; respectively.

In addition to electrically and optically separating the multicolorpixels 230 of the Quantum Photonic Imager device 200, the pixelsidewalls 235, being comprised of a dielectric material such as SiO₂with the metal vias 236 illustrated in FIG. 6C embedded within itsinterior, would also form optical barriers which would optically sealthe vertical edges of each of the portions of the optical confinementregions of the laser diode structure 250, 260 and 270 comprising eachmulticolor pixel 230. In other words, the insulation and metal contactlayers in between the laser diode structures 250, 260 and 270 togetherwith the insulation and contact vias within the pixels sidewalls 235would form an array of vertically stacked multicolor laser dioderesonators that are optically and electrically separated in thehorizontal as well as the vertical planes. Such an electrical andoptical separation would minimize any possible electrical or opticalcrosstalk between the pixels 230 and allows each pixel within the arrayas well as each laser diode within each pixel to be separatelyaddressable. The laser light output from each of the pixels 230 would beemitted vertically through the array of the vertical waveguides 290which are optically coupled to the optical confinement regions of eachof the vertically stacked laser diodes 231, 232, and 233 that form eachof the pixels 230.

FIG. 8A and FIG. 8B illustrate vertical and horizontal cross-sectionalviews; respectively, of one of the vertical waveguides 290 comprisingthe array of vertical waveguides of one of the pixels 230 of the QuantumPhotonic Imager device 200 of this invention. As illustrated in FIG. 8Aand FIG. 8B, each of the vertical waveguides 290 would be opticallycoupled along its vertical height with optical confinement regions ofthe three vertically stacked laser diodes 231, 232, and 233 comprisingthe pixel 230. As illustrated in FIG. 8A and FIG. 8B, each of thevertical waveguides 290 would be comprised of a waveguide core 291 whichwould be enclosed within a multilayer cladding 292. The array of pixel'swaveguides 290 would typically be etched through the Si-substrate 240side of the photonic multilayer structure 210, their interior would thenbe coated with the multilayer cladding 292 and the waveguides would thenbe refilled with the dielectric material to form the vertical waveguidecore 291. Although any appropriate semiconductor etching technique maybe used for etching the vertical waveguides 290, one exemplary etchingtechnique is a dry etching technique, such as chlorine-based,chemically-assisted ion beam etching (Cl-based CAIBE). However, otheretching techniques, such as reactive ion etching (RIE) or the like maybe used. Although any appropriate semiconductor coating technique may beused for forming the core 291 and the multilayer cladding 292 of thevertical waveguides 290, one exemplary layer deposition technique isplasma-assisted chemical vapor deposition (PE-CVD). The trenches etchedfor the vertical waveguides 290 preferably will have slightly slopedsides as illustrated in FIG. 8A in accordance with the increasingwavelength of the respective laser diodes in the laser diode stack.

As illustrated in FIG. 8A and FIG. 8B, each of the vertical waveguides290 would typically have a circular cross-section and its verticalheight would extend the thickness of the Si-substrate 240 plus thecombined thicknesses of the three vertically stacked laser diodes 231,232, and 233 comprising the pixel 230. Preferably the diameter (indexguiding diameter) of the pixel's vertical waveguides 290 at the centerof the coupling region with each of the laser diodes 231, 232, and 233would equal to the wavelength of the respective laser diode.

First Embodiment of the Vertical Waveguides

In one embodiment of the Quantum Photonic Imager device 200 of thisinvention the cores 291 of the pixel's vertical waveguides 290 would be“evanescence field coupled” to the optical confinement regions ofstacked laser diodes 231, 232, and 233 that form a single pixel 230. Inthis embodiment the vertical waveguide cladding 292 would be comprisedof an outer layer 293 of 50-nm to 100-nm thick of insulating material,such as SiO₂, and an inner layer 294 of highly reflective metal such asaluminum (Al), silver (Ag) or gold (Au). The core 291 of the verticalwaveguides 290 could either be air-filled or filled with a dielectricmaterial such as SiO₂, silicon nitride (Si₃N₄) or tantalum pentoxide(TaO₅). Through the evanescence field coupling of this embodiment, afraction of the laser light confined within the optical confinementregion of each of the laser diodes 231, 232, and 233 would be coupledinto the dielectric core 291 of the vertical waveguides 290 where itwould be guided vertically through reflections on the highly reflectivemetallic inner cladding layer 294 of the waveguide cladding 292.

In this embodiment of the Quantum Photonic Imager device 200 of thisinvention the coupling between the optical confinement regions ofstacked laser diodes 231, 232, and 233 comprising each of the pixels 230and its constituent vertical waveguide 290 would occur due to photontunneling across the metallic inner cladding layer 294. Such photontunneling would occur when the thickness of the reflective metallicinner cladding layer 294 of the waveguide cladding 292 is selected to besufficiently smaller than the penetration depth of evanescence fieldinto the reflective metallic inner cladding layer 294 of the waveguidecladding 292. In other words, the energy associated with the lightconfined within the optical confinement regions of stacked laser diodes231, 232, and 233 would be transmitted into metallic inner claddinglayer 294 a short distance before it returned into the opticalconfinement regions of stacked laser diodes 231, 232, and 233 and whenthe thickness of the reflective metallic layer 294 is sufficientlysmall, a portion of this energy would be coupled into the verticalwaveguide core 291 and would be guided vertically through reflections onthe highly reflective metallic inner cladding layer 294 of the waveguidecladding 292 and emitted perpendicular to the surface of the QuantumPhotonic Imager device 200.

The evanescence field transmitted from the optical confinement regionsof stacked laser diodes 231, 232, and 233 into the reflective metalliclayer 294 would decay exponentially and would have mean penetrationdepth “d” that is given by;d=λ/2π√{square root over (n ₀ ² sin²θ_(i) −n ₁ ²)}  (1)Where λ is the wavelength of the coupled light, n₀ and n₁ are therefractive index of the outer cladding layer 293 and the inner claddinglayer 294; respectively, and θ_(i) is the light angle of incidence fromoptical confinement regions of the laser diodes 231, 232 and 233 ontothe inner cladding layer 294.

As indicated by equation (1), for a given n₀, n₁ and θ_(i) theevanescence field penetration depth decreases with the decrease in thelight wavelength λ. In order to use one thickness value for the innercladding layer 294 that would effectively couple the three differentwavelengths generated by the laser diodes 231, 232, and 233, thethickness of the inner cladding layer 294 would be selected usingEquation (1) with the value of λ being the wavelength associated withshortest wavelength generated by stacked laser diodes 231, 232, and 233,being in the case of the aforementioned embodiment the wavelengthassociated with the blue laser diode 233. When the thickness of theinner cladding layer 294 is selected based on this criterion, the lightgenerated by the stacked laser diodes 231, 232, and 233 would be coupledinto the vertical waveguide 290 would be 0.492, 0.416 and 0.368;respectively, of the intensity of the light reflected by the interfacebetween optical confinement region of stacked laser diodes 231, 232, and233 and the vertical waveguide 290. When the thickness of inner claddinglayer 294 is increased, the amount of light coupled into the verticalwaveguide 290 will decrease proportionally. The reflectivity of theinner cladding layer 294 toward the optical confinement regions of thelaser diodes 231, 232, and 233 and toward the vertical waveguide core291 would be given; respectively, by:R ₀₁=└(n ₁ −n ₀)² +k ₁ ²┘/└(n ₁ −n ₀)² +k ₁ ²┘  (2.a)R ₁₂=└(n ₂ −n ₁)² +k ₁ ²┘/└(n ₂ −n ₁)² +k ₁ ²┘  (2.b)Where n₂ is the refractive index of the vertical waveguide core 291 andk₁ is the absorption coefficient of the inner cladding layer 294.

In the above exemplary embodiment of the evanescence field coupledvertical waveguides 290 of this invention in which SiO₂ is used as anouter cladding layer 293 and Si₃N₄ is used as the waveguide core 291material, a 50-nm thick silver (Ag) inner cladding 294 would coupleapproximately 36% of the laser light incident on the interface betweenthe optical confinement regions of the laser diodes 231, 232, and 233and the vertical waveguide 290 while achieving approximately 62%reflectivity within the interior of the vertical waveguides 290. Itshould be noted that the part of the light which is not coupled into thevertical waveguides 290 would either be absorbed by inner cladding 294(approximately 0.025) or would be recycled back into the opticalconfinement regions of the laser diodes 231, 232, and 233 where it wouldbe amplified by the active regions of laser diodes 231, 232, and 233 andthen re-coupled into the vertical waveguides 290.

Second Embodiment of the Vertical Waveguides

In another embodiment of the Quantum Photonic Imager device 200 of thisinvention the cores 291 of the pixel's vertical waveguides 290 would becoupled to the optical confinement regions of stacked laser diodes 231,232, and 233 that form a single pixel 230 through the use of anisotropicmultilayer thin cladding. What is meant by “anisotropic” in this contextis that the reflectance/transmittance characteristics would beasymmetric at either side of the interface between the verticalwaveguide 290 and the optical confinement regions of the stacked laserdiodes 231, 232, and 233. The simplest realization of this embodimentwould be to use a single thin cladding layer 293 having a refractiveindex value between that of the waveguide core 291 and the opticalconfinement regions of laser diodes 231, 232, and 233 and having thewaveguide core 291 preferably filled with a dielectric materialpreferably having a refractive index that is at least equal to that ofthe optical confinement regions of the stacked laser diodes 231, 232,and 233.

The reflectance and transmittance characteristics of thin dielectricmultilayer coatings are described in detail in Ref. [39]. At a normalangle of incidence, the reflectivity at the interface between theoptical confinement regions of laser diodes 231, 232, and 233 and thecladding layer 293 would be given by:R=[(n ₁ ² −n ₀ n ₁)/(n ₁ ² +n ₀ n ₁)]²  (3)Where n₀, n₁ and n₂ are the refractive index of the optical confinementregions of stacked laser diodes 231, 232, and 233, of the cladding layer293 and the waveguide core 291; respectively. As the angle of incidenceat the interface between the optical confinement regions of laser diodes231, 232, and 233 and the cladding layer 293 increases, the reflectivityincreases until all the light is totally reflected when the criticalangle is reached. Since, the critical angle depends on the ratio of therefractive index across the interface, when this ratio is selected suchthat the critical angle of the interface between the optical confinementregions of laser diodes 231, 232, and 233 and the cladding layer 293 islarger than the critical angle between the waveguide core 291 and thecladding layer 293, a portion of the light would be coupled into thewaveguide core 291 and would be index guided through total internalreflection (TIR) by the pixel's vertical waveguides 290 to be emittedperpendicular to the surface of the Quantum Photonic Imager device 200.

In the above exemplary embodiment of coupling of the vertical waveguides290 through the use of multilayer thin cladding in which anapproximately 100-nm thick of SiO₂ is used as a cladding layer 293 andtitanium dioxide (TiO₂) is used as the waveguide core 291 material,approximately 8.26% of the laser light incident on the interface betweenthe optical confinement regions of the laser diodes 231, 232, and 233and the vertical waveguide 290 would be coupled into the waveguide core291 and index guided through total internal reflection by the pixel'svertical waveguides 290 to be emitted perpendicular to the surface ofthe Quantum Photonic Imager device 200.

In comparison to the evanescence field coupling of the precedingembodiment, coupling of vertical waveguides 290 through the use ofmultilayer thin cladding would couple a lesser amount of the light fromthe optical confinement regions of stacked laser diodes 231, 232, and233 into the waveguide core 291, but the coupled light would notexperience any losses as it traverses the length of the verticalwaveguide 290 because the light is TIR-guided, hence approximately thesame amount of the light would be outputted through the verticalwaveguide 290 perpendicular to the surface of the Quantum PhotonicImager device 200. It should be noted that the part of the light whichis not coupled into the vertical waveguides 290 by inner cladding 293(which in the case of this example would be 91.74%) would be recycledback into the optical confinement regions of the laser diodes 231, 232,and 233 where it would be amplified by the active regions of laserdiodes 231, 232, and 233 and then re-coupled into the verticalwaveguides 290.

Although in the above exemplary embodiment of coupling of the verticalwaveguides 290 through the use of multilayer thin cladding only a singlelayer was exemplified, multiple thin cladding layers could be used toalter the ratio of the light intensity coupled into the verticalwaveguide 290 to that recycled back in the optical confinement regionsof the laser diodes 231, 232, and 233. For example when two thincladding layers are used with the outer cladding being 150-nm thickSi₃N₄ and the inner cladding being 100-nm thick SiO₂ in conjunction aTiO₂ waveguide core 291, approximately 7.9% of the laser light incidenton the interface between the optical confinement regions of the laserdiodes 231, 232, and 233 and the vertical waveguide 290 would be coupledinto the waveguide core 291 and TIR-guided by the pixel's verticalwaveguides 290 to be emitted perpendicular to the surface of the QuantumPhotonic Imager device 200. The selection of the number of thin claddinglayers used, their refractive index and thickness are design parametersthat could be utilized to fine tune the coupling characteristics of thepixel's vertical waveguides 290, and subsequently the overallperformance characteristics the Quantum Photonic Imager device 200.

Third Embodiment of the Vertical Waveguides 290

In another embodiment of the Quantum Photonic Imager device 200 of thisinvention the core 291 of the pixel's vertical waveguides 290 would becoupled to the optical confinement regions of stacked laser diodes 231,232, and 233 that form a single pixel 230 through the use of nonlinearoptical (NLO) cladding. The primary advantage of this embodiment is thatit would enable the Quantum Photonic Imager device 200 of this inventionto operate as a mode-locked laser emissive device (mode-locking enableslaser devices to emit ultra-short pluses of light). As a consequence ofthe mode-locked operation the Quantum Photonic Imager device 200 enabledby this embodiment, the Quantum Photonic Imager device 200 would achieveimproved power consumption efficiency and a higher peak-to-averageemitted light intensity. The mode-locked operation of this embodimentwould be incorporated within the cladding 292 of the pixel's verticalwaveguides 290 in conjunction with the vertical waveguide couplingmethod of the preceding embodiment.

This embodiment would be realized by adding a thin outer cladding layer295, herein after will be referred to as the gate cladding layer,between the optical confinement regions of stacked laser diodes 231,232, and 233 and the outer cladding layer 293 as illustrated in FIG. 8B.The gate cladding layer 295 would be a thin layer of an NLO materialsuch as single crystal poly PTS polydiacetylene (PTS-PDA) orpolydithieno thiophene (PDTT) or the like. The refractive index n ofsuch NLO materials is not a constant, independent of the incident light,but rather its refractive index changes with increasing the intensity Iof the incident light. For such NLO materials, the refractive index nobeys the following relationship to the incident light intensity:n=n ₀+χ⁽³⁾ I  (4)

In Equation (4) χ⁽³⁾ is the third order nonlinear susceptibility of theNLO material and n₀ is the linear refractive index value that the NLOmaterial exhibits for low values of the incident light intensity I. Inthis embodiment the linear refractive index n₀ and thickness of the NLOmaterial comprising the gate cladding layer 295 are selected such thatat low incident light intensity I, substantially all of the lightincident on the multilayer cladding 292 from the optical confinementregions of stacked laser diodes 231, 232, and 233 would be reflectedback and recycled into the optical confinement regions of the laserdiodes 231, 232, and 233 where it would be amplified by the activeregions of laser diodes 231, 232, and 233.

As the light intensity within the optical confinement regions of thelaser diodes 231, 232, and 233 increases due to the integration lightflux, the refractive index n of the gate cladding layer 295 would changein accordance with Equation (4), causing the ratio of the lightintensity that is recycled back into the optical confinement regions ofthe laser diodes 231, 232, and 233 to that coupled into the verticalwaveguide 290 to decrease, thus causing a portion of the light fluxintegrated within the optical confinement regions of the laser diodes231, 232, and 233 to be coupled into the vertical waveguide 290 andemitted perpendicular to the surface of the Quantum Photonic Imagerdevice 200.

As the light is coupled into the waveguide 290, the integrated lightflux within the optical confinement regions of the laser diodes 231,232, and 233 would decrease, causing the intensity I of the lightincident on the gate cladding layer 295 to decrease, which in turn wouldcause the refractive index n to change in accordance with Equation (4)causing the ratio of the light intensity that is recycled back into theoptical confinement regions of the laser diodes 231, 232, and 233 tothat that is coupled into the vertical waveguide 290 to increase, thuscausing the cycle of light flux integration within the opticalconfinement regions of the laser diodes 231, 232, and 233 to berepeated.

In effect the use of the multilayer cladding that incorporates an NLO ofthis embodiment would cause the optical confinement regions of thepixel's laser diodes 231, 232, and 233 to operate as photonic capacitorswhich would periodically integrate the light flux generated by thepixel's laser diodes 231, 232, and 233 between periods during which theintegrated light flux is coupled into the vertical waveguide 290 andemitted at the surface of the pixel 230 of the Quantum Photonic imagerdevice 200.

When NLO gate cladding layer 295 is used in conjunction with themultilayer thin cladding of the vertical waveguide 290 coupling examplesof the preceding embodiment, the coupling performance would becomparable except that the light coupled into the vertical waveguide 290and emitted at the surface of the pixel 230 would occur as a train ofpluses. When an NLO gate cladding layer 295 of PTS-PDA having athickness of approximately 100-nm is used in conjunction with anapproximately 100-nm thick of SiO₂ inner cladding 293 and titaniumdioxide (TiO₂) is used as the waveguide core 291 material, the lightpulses emitted from the surface of the pixel 230 would typically have aduration in the range of approximately 20-ps to 30-ps with aninter-pulse period in the range of approximately 50-ps to 100-ps. Theselection of the number of thin cladding layers used in conjunction withNLO gate cladding layer 295, their refractive index and thicknesses aredesign parameters that could be utilized to fine tune the couplingcharacteristics of the pixel's vertical waveguides 290 as well as thepulsing characteristics of the multicolor laser light emitted from thepixel 230 and subsequently the overall performance characteristics theQuantum Photonic Imager device 200.

Fourth Embodiment of the Vertical Waveguides 290

A fourth embodiment of vertical waveguides 290 may be seen in FIG. 2D.In this embodiment, waveguides terminate at the end of the opticalconfinement region of each laser diode, so that the waveguidesterminating at the laser diode positioned at the top of the stack wouldcouple light only from that laser diode and the waveguides terminatingat the second from the top laser diode in the stack would couple lightfrom first and second laser diodes and the waveguides terminating at thethird laser diode from the top of the stack would couple light from thefirst, second and third laser diodes in the stack. Preferably thesewaveguides would be straight, not tapered. These waveguides may also beair filled or filled with a suitable dielectric, such as SiO₂. Usingthese differing height waveguides the amount of light coupled from thefirst laser diode in the stack would be higher than that coupled fromthe second laser diode in the stack and the amount of light coupled fromthe second laser diode in the stack would be higher than that coupledfrom the third laser diode in the stack. Since a satisfactory colorgamut would include more green than red, and more red than blue, onemight place the green diode on top, the red in the middle and the blueon the bottom of the stack.

Pixel Waveguide Array

As explained in the preceding discussion, each of the pixels 230comprising the Quantum Photonic Imager device 200 would comprise aplurality of vertical waveguides 290 through which the laser lightgenerated by the pixel's laser diodes 231, 232, and 233 would be emittedin a direction that is perpendicular to the surface of the QuantumPhotonic Imager device 200. The plurality of pixel's vertical waveguides290 would form an array of emitters through which the light generatedthe pixel's laser diodes 231, 232, and 233 would be emitted. Given thevertical waveguides 290 light coupling methods of the preceding firstthree embodiments, the light emitted from each of the pixel's verticalwaveguides 290 would have a Gaussian cross-section having an angularwidth of approximately ±20 degrees at half its maximum intensity. In thepreferred embodiment of the Quantum Photonic Imager device 200, theplurality of the pixel's vertical waveguides 290 would be arranged in anumber and a pattern that is selected to reduce the maximum divergenceangle (collimation angle) of the light emitted from surface of the pixel230, to provide a uniform brightness across the area of the pixel, andto maximize pixel brightness.

In using well known theories of phased emitter arrays Ref. [41], theangular intensity of the light emitted by the pixels 230 within themeridian plane comprising N of the pixel's vertical waveguides 290 wouldbe given by;I(θ)=E(θ){J ₁ [aX(θ)]/aX(θ)}²{Sin [NdX(θ)]/Sin [dX(θ)]}²  (5.a)Where;X(θ)=(π Sin θ)/λ  (5.b)

J₁(.) the Bessel function, λ is the wavelength of the light emitted bythe pixel's vertical waveguides 290, α is the diameter of the verticalwaveguides 290, d is the center-to-center distance between the pixel'svertical waveguides 290 and E(θ) is the intensity profile of the lightemitted from each the pixel's vertical waveguides 290, which as statedearlier would typically be a Gaussian profile having an angular width ofapproximately ±20 degrees at half its maximum intensity. Preferably theparameter a, the diameter (index guiding diameter) of the pixel'svertical waveguides 290 at the center of the coupling region with eachof the laser diodes 231, 232, and 233 would equal to the wavelength ofthe respective laser diode. The typical value of the parameters, thecenter-to-center distance between the pixel's vertical waveguides 290,would be at least 1.2α and its specific value would be selected to finetune emission characteristics of the pixel 230.

FIG. 9A illustrates the angular intensity of the light emitted by 10×10micron pixels 230 comprising an array of 9×9 uniformly spaced verticalwaveguides 290, having a diameter α as specified above andcenter-to-center d=2α, within the meridian plane containing the diagonalof the pixel at the multiple values of wavelength emitted by the pixels230. Specifically, in FIG. 9A the profiles 910, 920 and 930 illustratethe angular intensity of the light emitted by the pixels 230 at the redwavelength (615-nm), the green wavelength (520-nm), and the bluewavelength (460-nm). As illustrated in FIG. 9A, the multicolor laserlight emitted by the pixel 230, and subsequently the Quantum Photonicimage 200, would have a tightly collimated emission pattern withcollimation angle well within ±5°, thus making the Quantum PhotonicImager device 200 to have an optical f/# of approximately 4.8.

The pattern of the vertical waveguides 290 within the pixel 230 surfacecould be tailored to achieve the required emission characteristics interms of the optical f/# for the Quantum Photonic Imager device 200. Theimportant design criterion in creating the pattern of the verticalwaveguides 290 is to generate a uniform emission at the required opticalf/# while retaining sufficient area for the pixel's light generatinglaser diodes 231, 232, and 233 after the array of vertical waveguides290 are etched. FIG. 9B illustrates several possible patterns of thevertical waveguides 290 within the pixel 230 surface that could be usedin conjunction with the Quantum Photonic Imager device 200 of thisinvention. Based on the teachings of this invention, a person skilled inthe art would know how to select the pattern of the vertical waveguides290 within the pixel 230 surface that would generate the light emissionoptical f/# that is best suited for the intended application of theQuantum Photonic Imager device 200 of this invention.

Digital Structure

FIG. 10A illustrates a vertical cross-section of the digitalsemiconductor structure 220 of the Quantum Photonic Imager device 200.The digital semiconductor structure 220 would be fabricated withconventional CMOS digital semiconductor techniques, and as illustratedin FIG. 10A, would be comprised of the multiple metal layers 222, 223,224 and 225, separated by thin layers of insulating semiconductormaterial such as SiO₂, and digital control logic 226 deposited usingconventional CMOS digital semiconductor techniques on the Si-substrate227.

As illustrated in FIG. 10B, the metal layer 222 would incorporate aplurality of pixel's contact pad patterns whereby each contact padpattern would be substantially identical to that of the pixel contactpad pattern of the photonic semiconductor structure 210 illustrated inFIG. 7. The plurality of pixel contact pad patterns of the metal layer222 would constitute the bonding interface between the photonicsemiconductor structure 210 and the digital semiconductor structure 220as explained earlier. The metal layer 222 would also incorporate at itsperiphery the device contact bonding pads 221 of the entire QuantumPhotonic Imager device 200 as illustrated in FIG. 2C.

FIG. 10C illustrates the layout of the metal layer 223 which incorporateseparate power and ground metal rails 310, 315 and 320 designated fordistributing power and ground to the pixel's red, green and blue laserdiodes 231, 232, and 233; respectively, and the metal rails 325 whichare designated for routing power and ground to the digital logic portionof the digital semiconductor structure 220. FIG. 10D illustrates thelayout of the metal layer 224 which incorporates separate metal tracesdesignated for distributing data 410, update 415 and clear 420 signalsto the digital control logic semiconductor structure 226 sectiondesignated for controlling the on-off states of the pixels' red, greenand blue laser diodes 231, 232, and 233, respectively. FIG. 10Eillustrates the layout of the metal layer 225 which incorporatesseparate metal traces designated for distributing the load 510 andenable 520 signals to the digital control logic semiconductor structure226 section designated for controlling the on-off states of the pixel'sred, green and blue laser diodes 231, 232, and 233, respectively.

The digital control logic semiconductor structure 226 would be comprisedof the pixels' digital logic section 228, which is positioned directlyunder the photonic semiconductor structure 210 (FIG. 2B), and thecontrol logic region 229 which is positioned at the periphery of thedigital logic region 228 as illustrated in FIG. 2C. FIG. 11A illustratesan exemplary embodiment of the control logic section 229 of the digitalcontrol logic semiconductor structure 226, which is designed to acceptred, green and blue PWM serial bit stream input data and clock signals425, 426, and 427, respectively, which are generated external to theQuantum Photonic Imager device 200, plus the control clock signals 428and 429, and covert the accepted data and clock signals into the controland data signals 410, 415, 420, 510 and 520 which are routed to thedigital logic section 228 via the interconnect metal layers 224 and 225.

The digital logic section 228 of the digital control logic semiconductorstructure 226 would be comprised of two dimensional arrays of pixelslogic cells 300 whereby each such logic cell would be positioneddirectly under one of the pixels 230 comprising the Quantum PhotonicImager device 200. FIG. 11B illustrates an exemplary embodiment of thedigital logic cell 300 comprising the digital logic section 228 of thedigital control logic semiconductor structure 226. As illustrated inFIG. 11B, the pixel logic cell 300 associated with each of the pixelscomprising the Quantum Photonic Imager device 200 would be comprised ofthe digital logic circuits 810, 815 and 820 corresponding with the red,green and blue pixel's laser diodes 231, 232, and 233, respectively. Asillustrated in FIG. 11B, the digital logic circuits 810, 815 and 820would accept the control and data signals 410, 415, 420, 510 and 520 andbased on the accepted data and control signals would enable connectivityof the power and ground signals 310, 315 and 320 to the red, green andblue pixel's laser diodes 231, 232, and 233, respectively.

The digital semiconductor structure 220 would be fabricated as amonolithic CMOS wafer that would incorporate a multiplicity of digitalsemiconductor structures 220 (FIG. 2A). As explained earlier, thedigital semiconductor structure 220 would be bonded with the photonicsemiconductor structure 220 using wafer-level direct bonding techniquesor the like to form an integrated multi wafer structure which would thenbe etched at the periphery of each single Quantum Photonic Imager device200 die area in order to expose the device contact bonding pads 221,then would be cut into individual Quantum Photonic Imager device 200dies illustrated in FIG. 2A and FIG. 2C. Alternatively, the digitalsemiconductor 210 wafer would be cut into dies and separately thephotonic semiconductor structure 210 wafer would also be cut into dies,each having an area that contains the required number of pixel's laserdiodes 231, 232, and 233, and then each the photonic semiconductorstructure 210 die would be die-level bonded using flip-chip techniquesor the like to the digital semiconductor 210 die to form a singleQuantum Photonic Imager device 200 illustrated in FIG. 2A and FIG. 2C.

QPI Fabrication Flow

FIG. 12 is a flow chart that illustrates the semiconductor process flowthat would be used to fabricate the Quantum Photonic Imager device 200in accordance with the exemplary embodiment described in the precedingparagraphs. As illustrated in FIG. 12, the process starts with step S02and continues to step S30, during which various wafers are bonded, andinsulation and metal layers are deposited, interconnect vias, sidewallsand vertical waveguides are formed. It should be noted that thesemiconductor fabrication flow of the laser diode multilayersemiconductor structures 250, 260 and 270 as well as the digitalsemiconductor structure 220 would be performed separately and externalto the fabrication process flow illustrated in FIG. 12, which is meantto illustrate an exemplary embodiment of the semiconductor process flowof bonding these wafers and forming the pixel structures 230 andinterconnects.

In step S02 the SiO₂ insulation layer 241 would be deposited on the baseSi-substrate 240 wafer. In step S04 the p-contact metal layer would bedeposited and in step S06 the formed stack would be bonded with laserdiode multilayer semiconductor wafer and the laser diode wafer is etcheddown to the stop-etch layer. In step S08 the pixel sidewalls trenchesare double etched first down to the insulation layer preceding the metallayers deposited in step S04 then down to the metal layer deposited instep S04 and the etched trenches are then refilled with SiO₂. In stepS10 the trenches for the pixels vertical contact vias are etched down tothe metal layer deposited in step S04 then a thin insulation layer isdeposited and etched to expose the deposited vias. In step S12 then-contact metal layer would be deposited then etched to extend theheight of the pixels' sidewall trenches. In step S14 an insulation layerof SiO₂ is deposited then the process flow of steps S04 through S14 isrepeated for each of the laser diode multilayer semiconductor wafersthat would be incorporated into the Quantum Photonic Imager device 200.

In step S16 the metal layer required for forming the bonding contact pad700 is deposited then etched to form the contact pad pattern illustratedin FIG. 7. In step S20 the vertical waveguides 290 are etched throughthe Si-substrate side of the formed multilayer structure to form thepixels' 230 waveguide pattern such as those illustrated in FIG. 9B. Instep S22 the waveguide cladding layers 292 are deposited and then thewaveguide cavities are refilled with the waveguide core 291 material instep S24. In step S26 the Si-substrate side of the formed multi-layerlaser diode structure is polished to optical quality and coated asrequired to form the emissive surface of the Quantum Photonic Imagerdevice 200. Steps S02 through S28 would result in a wafer-size photonicsemiconductor structure 210 which would be wafer-level pad-side bondedwith the digital semiconductor structure 220 wafer in step S28.

In step S30 the resultant multi-wafer stack is etched to expose thecontact pads 221 of the individual dies Quantum Photonic Imager device200 and the multi-wafer stack is cut into individual dies of the QuantumPhotonic Imager device 200.

An alternative approach to the process of step S30 would be to cut thephotonic semiconductor structure 210 formed by the process steps S02through S26 into the die size required for the Quantum Photonic imagerdevice 200 and separately cut the digital semiconductor structure 220wafer into dies then pad-side bond the two dies using flip-chiptechnique to form the individual dies of the Quantum Photonic Imagerdevice 200.

QPI Projector

The Quantum Photonic Imager device 200 would typically be used as adigital image source in digital image projectors used in front or rearprojection display systems. FIG. 13 illustrates an exemplary embodimentof a typical digital image projector 800 that incorporates the QuantumPhotonic Imager device 200 of this invention as a digital image source.The Quantum Photonic Imager device 200 would be integrated on a printedcircuit board together with a companion digital device 850 (which willbe referred to as the image data processor and will be functionallydescribed in subsequent paragraphs) that would be used convert thedigital image input into the PWM formatted input to the Quantum PhotonicImager device 200. As illustrated in FIG. 13, the emissive opticalaperture of the Quantum Photonic Imager device 200 would be coupled witha projection optics lens group 810 which would magnify the imagegenerated by the Quantum Photonic Imager device 200 to the requiredprojection image size.

As explained earlier, the light emitted from Quantum Photonic Imagerdevice 200 would typically be contained within an optical f/# ofapproximately 4.8, which makes it possible to use few lenses (typically2 or 3 lenses) of moderate complexity to achieve source imagemagnification in the range between 20 to 50. Typical digital projectorsthat use existing digital imagers such as micro-mirror, LCOS or HTPSimager devices having an optical f/# of approximately 2.4, wouldtypically requires as many as 8 lenses to achieve a comparable level ofsource image magnification. Furthermore, typical digital projectors thatuse passive (meaning reflective or transmissive type) digital imagerssuch as micro-mirror, LCOS or HTPS imager devices would require acomplex optical assembly to illuminate the imager. In comparison, sincethe Quantum Photonic Imager device 200 is an emissive imager, thedigital image projector 800 which uses the Quantum Photonic Imagerdevice 200 would not require any complex optical illumination assembly.The reduced number of lenses required for magnification plus theelimination of the illumination optics would make the digital imageprojector 800 which uses the Quantum Photonic Imager device 200substantially less complex and subsequently more compact and less costlythan digital projectors that use existing digital imagers such asmicro-mirror, LCOS or HTPS imager devices.

OPI Device Efficiency

An important aspect of the Quantum Photonic Imager device 200 of thisinvention is its luminance (brightness) performance and itscorresponding power consumption. A single 10×10 micron pixel 230 havingthe laser diode structures 231, 232, and 233 of the preceding exemplaryembodiment as specified in FIG. 4A, FIG. 4B and FIG. 4C, respectively,would consume approximately 4.5 μW, 7.4 μW and 11.2 μW to generate aradiant flux of approximately 0.68 μW, 1.1 μW and 1.68 μW of red(615-nm), green (520-nm) and blue (460-nm); respectively, which equatesto 1 milli lumen of luminous flux at color temperature of 8,000 K°. Inother words, the single 10×10 micron pixel 230 of the Quantum PhotonicImager device 200 would consume approximately 23 μW to generateapproximately 1 milli lumen of luminous flux at color temperature of8,000 K°, which would be sufficient to provide a brightness of more than1,200 candela/meter² when the pixel is magnified to 0.5×0.5 millimeter.At the brightness provided by most existing commercial displays, whichtypically ranges between 350 candela/meter² to 500 candela/meter², thesingle 10×10 micron pixel 230 of the Quantum Photonic Imager device 200when magnified in size to 0.5×0.5 millimeter would consume less than 10μW, which is nearly one and a half orders of magnitude less than thepower consumption required by existing commercial displays such as PDP,LCD or projection displays that use a micro-mirrors, LCOS or HTPSdevices.

As a direct result of the elimination of the inefficiencies associatedwith illumination optics and the imager optical coupling required in allprojectors that use existing digital imagers such as micro-mirror, LCOSor HTPS imager devices, the Quantum Photonic Imager device 200 of thisinvention would achieve substantially higher efficiency when compared toexisting digital imagers. Specifically, the losses associated with thedigital projector 800 illustrated in FIG. 13 that uses the QuantumPhotonic Imager 200 of this invention would be limited to the losses dueto projection optics lens group 810, which would approximately be about4%. Meaning that the efficiency of the digital projector 800 illustratedin FIG. 13 that uses the Quantum Photonic Imager 200 in terms of theratio of projected luminous flux to the generated luminous flux would beapproximately 96%, which is substantially higher than the efficiency ofless than 10% achieved by projectors that use existing digital imagerssuch as micro-mirror, LCOS or HTPS imager devices.

For example, the digital projector 800 illustrated in FIG. 13 that usesthe Quantum Photonic Imager 200 of this invention having one millionpixels would consume approximately 25.4 watts to generate approximately1,081 lumens of luminous flux at color temperature of 8,000 K°, whichwould be sufficient to project an image having 60″ diagonal at abrightness of approximately 1,000 candela/meter² on a front projectionscreen. When the efficiency of a typical projection screen is takinginto account, the cited example of the digital projector 800 wouldproject an image with brightness of approximately 560 candela/meter² ona rear projection screen. For comparison purposes the power consumptionof a typical existing rear projection displays that achieve brightnessin the range of 350 candela/meter² would be in excess of 250 watts,which indicates that the digital projector 800 that uses the QuantumPhotonic Imager 200 as an image source would achieve a much higherprojected image brightness than existing front and rear projectiondisplays, yet at a substantially lower power consumption.

OPI Advantages & Applications

The compactness and low cost characteristics of the digital imageprojector 800 which uses the Quantum Photonic Imager device 200 whencombined with the low power consumption of the Quantum Photonic Imagerdevice 200 would make it possible to design and fabricate digital imageprojectors that can be effectively embedded in mobile platforms such ascell phones, laptop PC or comparable mobile devices. In particular, thedigital projector 800 that uses the Quantum Photonic Imager 200 of thisinvention such as that illustrated in FIG. 13 having 640×480 pixels anddesigned to achieve ±25 degrees projection field of view would achieveapproximately 15×15 mm volume and would consume less than 1.75 watts toproject 18″ projected image diagonal with brightness of approximately200 candela/meter² (for reference purposes, the typical brightness of alaptop PC is approximately 200 candela/meter²).

Because of its compactness and low power consumption, the QuantumPhotonic Imager 200 of the invention would also be suitable for near-eyeapplications such as helmet-mounted displays and visor displays.Furthermore, because of its ultra-wide gamut capabilities, the QuantumPhotonic Imager 200 of the invention would also suitable forapplications requiring realistic image color rendition such as simulatordisplays and gamming displays.

QPI Operation

With its pixel-based laser light generating capabilities described inthe preceding paragraphs, the Quantum Photonic Imager device 200 will beable to convert the digital source image data received from an externalinput into an optical image which would be coupled into the projectionoptics of the projector 800 as illustrated in FIG. 13. In using theQuantum Photonic Imager device 200 of this invention to synthesize thesource image, the luma (brightness) and chroma (color) components ofeach of the image pixels would be simultaneously synthesized throughapportioned setting of the on/off duty cycle of the correspondingpixel's red, green and blue laser diodes 231, 232, and 233.Specifically, for each of the source image pixels, the chroma componentof the pixel would be synthesized by setting the corresponding pixel'sred, green and blue laser diodes 231, 232, and 233 on/off duty cyclerelative ratios that reflect the required color coordinates for thepixel. Similarly, for each of the source image pixels, the lumacomponent of the pixel would be synthesized by setting the on/off dutycycle of the corresponding pixel's light generating red, green and bluelaser diodes 231, 232, and 233 collective on/off duty cycle values thatreflect the required brightness for the pixel. In other words, thepixel's luma and chroma components of each of the source image pixelswould be synthesized by controlling the on/off duty cycle and thesimultaneity of the corresponding pixel's light generating red, greenand blue laser diodes 231, 232, and 233 of the Quantum Photonic Imagerdevice 200.

By controlling the on/off duty cycle and simultaneity of the pixel'slaser diodes 231, 232, and 233 having the selected wavelengths of theexemplary embodiment of the Quantum Photonic Imager device 200 describedin the preceding paragraphs of 615-nm for the pixel's red laser diodes231, 520-nm for the pixel's green laser diode 232, and 460-nm for thepixel's blue laser diode 233, the Quantum Photonic Imager device 200 ofthis invention would be able to synthesize any pixel's color coordinatewithin its native color gamut 905 illustrated in FIG. 14A in referenceto the CIE XYZ color space. Specifically, the aforementioned operationalwavelengths of the exemplary embodiment of the Quantum Photonic Imagerdevice 200 pixel's laser diodes 231, 232, and 233 would define thevertices 902, 903 and 904; respectively, of its native color gamut 905as illustrated in FIG. 14A in reference to the CIE XYZ color space.

The specific color gamut of the source image would typically be based onimage color standards such as NTSC and HDTV standards. For comparisonpurposes, the display color gamut standards of NTSC 308 and HDTV 309 arealso shown on FIG. 14A as a reference to illustrate that the nativecolor gamut 305 of the exemplary embodiment the Quantum Photonic Imagerdevice 200 defined by the color primaries wavelengths for red at 615-nm,green at 520-nm and blue at 460-nm would include the NTSC 308 and HDTV309 color gamut standards and would extend beyond these color gamutstandards by a significant amount.

Given the extended native color gamut 305 of the Quantum Photonic Imagerdevice 200 illustrated in FIG. 14A, the source image data would have tobe mapped (converted) from its reference color gamut (such as thatillustrated in FIG. 14A for the NTSC 308 and the HDTV 309 color gamut)to the native color gamut 305 of the Quantum Photonic Imager device 200.Such a color gamut conversion would be accomplished by applying thefollowing matrix transformation on the [R, G, and B] components of eachof the source image pixels:

$\begin{matrix}{\begin{bmatrix}R_{QPI} \\G_{QPI} \\B_{QPI}\end{bmatrix} = {M \cdot \begin{bmatrix}R \\G \\B\end{bmatrix}}} & (6)\end{matrix}$Where the 3×3 transformation matrix M would be computed from thechromaticity values of the coordinates of the white point and colorprimaries of the source image color gamut and the coordinates of thewhite point and color primaries 902, 903 and 904 (FIG. 14B) of theQuantum Photonic Imager device 200 within a given the reference colorspace, such as CIE XYZ color space for example. The result of the matrixtransformation defined by Equation (6) would define the components ofthe source image pixel [R_(QPI), G_(QPI), B_(QPI)] with respect to thenative color gamut 305 of the Quantum Photonic Imager device 200.

FIG. 14B illustrates the result of the matrix transformation defined byEquation (6) to define the components of the source image pixel[R_(QPI), G_(QPI), B_(QPI)] of two exemplary pixels 906 and 907 withrespect to the Quantum Photonic Imager device 200 native color gamut 305defined by the vertices 902, 903 and 904. As illustrated in FIG. 14B,the values [R_(QPI), G_(QPI), B_(QPI)] could span the entire color gamut305, enabling the Quantum Photonic Imager device 200 to synthesize thepixels [R, G, B] values of a source image that have a much wider colorgamut than that offered by the NTSC 308 and the HDTV 309 color gamut(FIG. 14A). As wider color gamut standards and wide-gamut digital imageand video input content becomes available, digital projectors 800 thatuse the Quantum Photonic Imager 200 of this invention would be poised toproject source images and video content in such wide-gamut format. Inthe interim, the wide-gamut capabilities of the Quantum Photonic Imager200 would allow it to synthesize digital image and video inputs with theexisting color gamut (such as NTSC 308 and the HDTV 309 color gamut) atan even lower power consumption than the exemplary values cited in anearlier paragraph.

The [R, G, B] values of every pixel in the source image would be mapped(converted) to the native color gamut 305 (color space) of the QuantumPhotonic Imager device 200 using the transformation defined by Equation(6). Without loss of generality, in assuming that the white point of thesource image has an [R, G, B]=[1, 1, 1], a condition which can always bemet by dividing [R, G, B] values of every pixel in the source image bythe white point's [R, G, B] value, the result of the transformationdefined by Equation (6) for each of the source image pixels would be avector [R_(QPI), G_(QPI), B_(QPI)] with values ranging between [0, 0, 0]for black and [1, 1, 1] for white. The above representation has thebenefit that the distances within the reference color space, such as CIEXYZ color space for example, between the pixel's and the color primaries902, 903 and 904 of the native gamut 305 of the Quantum Photonic Imagerdevice 200 defined by the values [R_(QPI), G_(QPI), B_(QPI)] would alsodefine the on/off duty cycles values for its respective red, green, andblue laser diodes 231, 232, and 233:λ_(R)=R_(QPI)λ_(G)=G_(QPI)  (7)λ_(B)=B_(QPI)Where λ_(R), λ_(G), and λ_(B) denote the on/off duty cycles of therespective pixel 230 of the Quantum Photonic Imager device 200 red,green, and blue laser diodes 231, 232, and 233; respectively, requiredto synthesize [R, G, B] values of each of the pixels comprising thesource image.

Typical source image data input, whether static images or dynamic videoimages, would be comprised of image frames which are inputted at a framerate, for example either 60 Hz or 120 Hz. For a given source image framerate, the on-time of the respective pixel 230 of the Quantum PhotonicImager device 200 red, green, and blue laser diodes 231, 232, and 233;respectively, required to synthesize the [R, G, B] values of sourceimage pixel would be the fraction of the frame duration defined by thevalues λ_(R), λ_(G), and λ_(B).

In order to account for possible pixel-to-pixel brightness variationsthat could result from possible variations in the semiconductor materialcharacteristics comprising the photonic semiconductor structure 210,during testing of the Quantum Photonic Imager device 200 which wouldtypically occur at the completion of the device fabrication stepsdescribed earlier, the device luminance profile would be measured and abrightness uniformity weighting factor would be calculated for eachpixel. The brightness uniformity weighting factors would be stored as alook-up-table (LUT) and applied by the Quantum Photonic Imager device200 companion image data processor 850. When these brightness uniformityweighting factors are taken into account, the on-time for each of thepixel 230 of the Quantum Photonic Imager device 200 would be given by:Λ_(R)=K_(R)λ_(R)Λ_(G)=K_(G)λ_(G)  (8)Λ_(B)=K_(B)λ_(B)Where K_(R), K_(G) and K_(B) are the brightness uniformity weightingfactors for each of the Quantum Photonic Imager device 200 pixel's red,green, and blue laser diodes 231, 232, and 233; respectively.

The on-time values of the red, green, and blue laser diodes 231, 232,and 233 of each of the pixels 230 comprising the Quantum Photonic Imagerdevice 200 expressed by Equation (8) would be converted into serial bitstreams using conventional pulse width modulation (PWM) techniques andinputted to the Quantum Photonic Imager device 200 at the frame rate ofthe source image together with the pixel address (row and column addressof the respective pixel within the array of pixels comprising theQuantum Photonic Imager device 200) and the appropriate synchronizationclock signals.

The conversion of the image source data into the input signals requiredby the Quantum Photonic Imager device 200 would be performed by thecompanion image data processor 850 in accordance with Equations (6)through (8). FIG. 15A and FIG. 15B illustrate a block diagram of theQuantum Photonic image data processor 850 and the timing diagramassociated with its interface with the Quantum Photonic Imager device200; respectively. Referring to FIG. 15A and FIG. 15B, the SYNC &Control block 851 would accept the frame synchronization input signal856 associated with the source image or video input and generate theframe processing clock signal 857 and the PWM clock 858. The PWM clock858 rate would be dictated by the frame rate and word length of thesource image or video input. The PWM clock 858 rate illustrated in FIG.15B reflects an exemplary embodiment of the Quantum Photonic Imager 200and companion Image Data Processor 850 operating at a frame rate of 120Hz and word length of 16-bit. A person skilled in the art would know howto use the teachings of this invention to make the Quantum PhotonicImager 200 and its companion Image data Processor 850 support sourceimage or video inputs having frame rates and word lengths that differfrom those reflected in FIG. 15B.

In synchronism with the frame clock signal 857, the Color-SpaceConversion block 852 would receive each frame of the source image orvideo data, and using the source input gamut coordinates, would performthe digital processing defined by Equations (6) to map each of thesource input pixel [R, G, B] values to the pixel coordinate values[R_(QPI), G_(QPI), B_(QPI)]. Using the white-point coordinates of thesource image or video data input, the Color-Space Conversion block 852would then convert each of the pixel values [R_(QPI), G_(QPI), B_(QPI)]using Equation (7) to the on/off duty cycle values λ_(R), λ_(G), andλ_(B) of the red, green, and blue laser diodes 231, 232, and 233,respectively, of the corresponding pixel 230 of Quantum Photonic Imager200.

The values λ_(R), λ_(G), and λ_(B) would then be used by the UniformityCorrection block 853 in conjunction with the pixel brightness weightingfactor K_(R), K_(G) and K_(B) stored in the Uniformity Profile LUT 854to generate the uniformity corrected on-time values [Λ_(R), Λ_(G),Λ_(B)] for each of the pixels 230 of the Quantum Photonic Imager 200using equation (8).

The values [Λ_(R), Λ_(G), Λ_(B)] generated by the Uniformity Correctionblock 853, which would typically be expressed in three 16-bit words foreach pixel, are then converted by the PWM Conversion block 855 into athree serial bit streams that would be provided to the Quantum PhotonicImager 200 in synchronism with the PWM clock. The three PWM serial bitstreams generated by the PWM Conversion block 855 for each of the pixels230 would provide the Quantum Photonic Imager device 200 with 3-bitwords, each of which define the on-off state of the pixel's lightgenerating red, green and blue laser diodes 231, 232, and 233 within theduration of the PWM clock signal 858. The 3-bit word generated by thePWM Conversion block 855 would be loaded into the appropriate pixeladdress of the digital semiconductor structure 220 of the QuantumPhotonic Imager device 200 and would be used, as explained earlier, toturn on or off the respective pixel's red, green and blue laser diodes231, 232, and 233 within the duration defined by the PWM clock signal858.

In the preceding exemplary embodiment of the operation of the QuantumPhotonic Imager device 200 of this invention, the source image pixelscolor and brightness specified by the pixel [R, G, B] values would bedirectly synthesized for each individual pixel in the source image usingthe color primaries 902, 903 and 904 of the native gamut 305 of theQuantum Photonic Imager device 200. Because the individual pixelbrightness and color are directly synthesized, this operational mode ofthe Quantum Photonic Imager device 200 is referred to as Direct-ColorSynthesize Mode. In an alternative exemplary embodiment of the operationof the Quantum Photonic Imager device 200 the color primaries of thesource image color gamut are first synthesized using the color primaries902, 903 and 904 of the native gamut 305 of the Quantum Photonic Imagerdevice 200 and the pixel color and brightness are then synthesized usingthe synthesized color primaries of the source image color gamut. In thisoperational mode of the Quantum Photonic Imager device 200, the pixel'sred, green and blue laser diodes 231, 232, and 233 collectively wouldsequentially synthesize the RGB color primaries of the source image.This would be accomplished by dividing the frame duration into threesegments whereby each segment would be dedicated for generating one ofthe color primaries of the source image and having the default values(white-point) of each of the pixel's red, green and blue laser diodes231, 232, and 233 reflect the coordinates of one of the source imagecolor primaries in each of the frame segments sequentially. The durationof the frame dedicated to each color primary segment and the relativeon-time values of the pixel's red, green and blue laser diodes 231, 232,and 233 during that segment would be selected based on the requiredwhite-point color temperature. Because the individual pixel brightnessand color are sequentially synthesized, this operational mode of theQuantum Photonic Imager device 200 is referred to as Sequential-ColorSynthesize Mode.

In the Sequential-Color Synthesize Mode of the Quantum Photonic Imagerdevice 200, the total number of PWM clock cycles within the frame wouldbe apportioned into three color primaries sub-frames, with one sub-framededicated to the R-primary, the second dedicated for the G-primary andthe third dedicated for the B-primary of the source image gamut. Theon-time of each the Quantum Photonic Imager device 200 pixel's red,green and blue laser diodes 231, 232, and 233 during the R-primarysub-frame, G-primary sub-frame and the B-primary sub-frame would bedetermined based on the distances within the reference color spacebetween the source image color primaries and the color primaries of theQuantum Photonic Imager device 200 native color gamut. These on-timevalues would then be modulated sequentially with [R, G, and B] values ofthe respective pixel of the source image.

The difference between Direct-Color Synthesize mode and Sequential-ColorSynthesize mode of the Quantum Photonic Imager device 200 is illustratedin FIG. 15B which shows the enable signal that would be provided to thepixel's red, green and blue laser diodes 231, 232, and 233 in each case.The sequence of enable signals 860 illustrate the operation of thepixel's red, green and blue laser diodes 231, 232, and 233 in theDirect-Color Synthesize mode where the pixel's luma and chromacomponents of the source image pixels would be directly synthesized bycontrolling the on/off duty cycle and simultaneity of the correspondingpixel's red, green and blue laser diodes 231, 232, and 233. The sequenceof enable signals 870 illustrate the operation of the pixel's red, greenand blue laser diodes 231, 232, and 233 in the Sequential-ColorSynthesize mode where the primaries of the source image gamut would besynthesized using the color primaries 902, 903 and 904 of the nativegamut 305 and luma and chroma components of the source image pixelswould be synthesized sequentially using the synthesized primaries of thesource image gamut.

The Direct-Color Synthesize mode and Sequential-Color Synthesize mode ofthe Quantum Photonic Imager device 200 would differ in terms of theachieved operating efficiency of the device as they would tend torequire different peak-to-average power driving conditions to achievecomparable level image brightness. However in both operational modes theQuantum Photonic Imager device 200 of this invention would be able tosupport comparable source image frame rate and [R, G, B] word length.

QPI Dynamic Range, Response Time, Contrast and Black Level

The dynamic range capability of the Quantum Photonic Imager device 200(defined as the total number of grayscale levels that can be generatedin the synthesize for each of the source image pixels) would bedetermined by the smallest value of PWM clock duration that can besupported, which in turn would be determined by the on-off switchingtime of the pixel's red, green and blue laser diodes 231, 232, and 233.The exemplary embodiment of the photonic semiconductor structure 210(FIG. 2A) described in the preceding paragraphs would achieve on-offswitching time that is a fraction of a nanosecond in duration, makingthe Quantum Photonic Imager device 200 able to readily achieve a dynamicrange of 16-bit. For comparison, most currently available displaysystems operate at 8-bit dynamic. Furthermore, the on-off switching timeof a fraction of a nanosecond in duration that can be achieved by thephotonic semiconductor structure 210 would also enable of the QuantumPhotonic Imager device 200 to achieve a response time that is a fractionof a nanosecond in duration. For comparison, the response time that canbe achieved by LCOS and HTPS type imagers is typically in the order of 4to 6 milliseconds and that of the micro mirror type imager is typicallyin the order of one microsecond. The imager response time plays acritical role in the quality of the image that can be generated by thedisplay system, in particular for generating video images. Therelatively slow response time of the LCOS and HTPS type imagers wouldtend to create undesirable artifacts in the generated video image.

The quality of a digital display is also measured by the contrast andblack level it can generate, with the contrast being a measure of therelative levels of white and black regions within the image and blacklevel being the maximum black that can be achieved in response to ablack filed input. Both the contrast and the black level of a displayare significantly degraded in existing projection displays that useimagers such as micro mirror, LCOS or HTPS imager because of thesignificant levels of photonic leakage associated with such imagers. Thehigh photonic leakage typical to these types of imager is caused bylight leaking from the on-state of the imager pixel onto its off-state,thus causing the contrast and black levels to degrade. This effect ismore pronounced when such imagers are operated in a color sequentialmode. In comparison the Quantum Photonic Imager device 200 would have nophotonic leakage since its pixel's red, green and blue laser diodes 231,232, and 233 on-state and off-states are substantially mutuallyexclusive making, the contrast and black levels that can be achieved bythe Quantum Photonic Imager device 200 orders of magnitude superior towhat can be achieved by micro mirror, LCOS or HTPS imagers.

In summary, the Quantum Photonic Imager device 200 of the presentinvention overcomes the weaknesses of other imagers plus exhibits thefollowing several advantages:

1. It requires low power consumption because of its high efficiency;

2. It reduces the overall size and substantially reduces the cost of theprojection system because it requires simpler projection optics and doesnot require complex illumination optics;

3. It offers extended color gamut making it is able to support thewide-gamut requirements of the next generation display systems; and

4. It offers fast response time, extended dynamic range, plus highcontrast and black levels, which collectively would substantiallyimprove the quality of the displayed image.

In the forgoing detailed description, the present invention has beendescribed with reference to specific embodiments thereof. It will,however, be evident that various modifications and changes can be madethereto without departing from the broader spirit and scope of theinvention. The design details and drawings are, accordingly, to beregarded in an illustrative rather than a restrictive sense. Skilledpersons will recognize that portions of this invention may beimplemented differently than the implementation described above for thepreferred embodiment. For example, skilled persons will appreciate thatthe Quantum Photonic Imager device 200 of this invention can beimplemented with numerous variations to the number of multilayer laserdiodes comprising the photonic semiconductor structure 210, the specificdesign details of the multilayer laser diodes 250, 260 and 270, thespecific design details of the vertical waveguides 290, specific designdetails associated with the selection of the specific pattern of thepixel's vertical waveguides 290, the specific details of thesemiconductor fabrication procedure, the specific design details of theprojector 800, the specific design details of the companion Image DataProcessor device 850, the specific design details of the digital controland processing required for coupling the image data input to the QuantumPhotonic device 200, and the specific design details associated with theselected operational mode of the chip-set comprising the QuantumPhotonic Imager 200 and its companion Image Data Processor 850. Skilledpersons will further recognize that many changes may be made to thedetails of the aforementioned embodiments of this invention withoutdeparting from the underlying principles and teachings thereof. Thescope of the present invention should, therefore, be determined only bythe following claims.

1. The method of making a two dimensional array of multicolor laseremitting pixels wherein each multicolor laser emitting pixel comprises aplurality of laser diode semiconductor structures, each for emitting adifferent color, stacked vertically with a grid of vertical sidewallselectrically and optically separating each multicolor pixel fromadjacent multicolor pixels within the array of multicolor pixels, and aplurality of vertical waveguides optically coupled to the laser diodesemiconductor structures to vertically emit laser light generated by thelaser diode semiconductor structures from a first surface of the stackof laser diode semiconductor structures; the method comprising: a)forming laser diode semiconductor structures of different colors, eachhaving multiple semiconductor layers of one or more of the followingsemiconductors alloy materials: Al_(x)In_(1-x)P,(Al_(x)Ga_(1-x))_(y)In_(1-y)P, Ga_(x)In_(1-x)P, Al_(x)Ga_(1-x)N,Al_(x)Ga_(1-x)N/GaN, In_(x)Ga_(1-x)N, GaN, each formed on a separatewafer over a thick substrate layer of either GaAs, GaN or InGaN, eachincluding an n-type etch-stop layer and a p-type contact layer of thesame respective semiconductor substrate layer material type, eachcomprising n-type and p-type waveguide layers and cladding layers thatdefine their respective optical confinement regions, each having atleast one quantum well surrounded by two barrier layers that definetheir respective active regions, and each comprising an electron blockerlayer embedded either within their respective p-type waveguide layers orbetween their respective p-type waveguide and cladding layers; b)depositing a SiO₂ layer upon a Si-substrate wafer; c) depositing ann-contact metal layer over the SiO₂ layer; d) wafer-level bonding of thep-type contact layer of a laser diode semiconductor structure wafer ofone color to the deposited n-contact metal layer and etching its GaAs,GaN or InGaN thick substrate down to its n-type etch-stop layer; e)etching a grid of trenches with vertical sidewalls down to the n-contactmetal layer and backfilling the etched trenches with SiO₂; f) etchingthe trenches for vertical interconnect metal vias and backfilling etchedtrenches with metal; g) depositing a p-contact metal layer and etchingthe sidewall trenches; and h) depositing another SiO₂ layer; i)repeating b) through h) for each additional color of laser diodesemiconductor structure to be incorporated within the two dimensionalarray of multicolor laser emitting pixels; j) depositing and etching ametal layer to form contact pads and refilling etched gaps with SiO₂; k)etching openings for the vertical waveguides though the Si-substrateside; l) depositing thin cladding layers on the interior walls ofopenings; and m) either backfilling the interior of the openingsremaining internal to the thin cladding layers with a dielectricmaterial of leaving then air filled.
 2. A method of making emissivemulticolor digital image fowling devices comprising: a) forming a waferof two dimensional arrays of multicolor laser emitting pixels wherebyeach multicolor laser emitting pixel comprises a plurality of laserdiode semiconductor structures, each for emitting a different color,stacked vertically with a grid of vertical sidewalls electrically andoptically separating each multicolor pixel from adjacent multicolorpixels within the array of multicolor pixels, a plurality of verticalwaveguides optically coupled to the laser diode semiconductor structuresto vertically emit laser light generated by the laser diodesemiconductor structures from a first surface of the stack of laserdiode semiconductor structures, and a plurality of contact padsproviding electrical contact to each laser diode semiconductorstructure; b) forming a wafer of digital semiconductor structures, eachhaving a plurality of digital semiconductor circuits in the respectivedigital semiconductor structure, each electrically coupled to receivecontrol signals from the periphery of the digital semiconductorstructure and electrically coupled to contact pads to separately controlon/off states of each of the multicolor laser diode semiconductorstructures that may be connected thereto; c) wafer-level bonding thewafer of two dimensional arrays of multicolor laser emitting pixels andthe wafer of digital semiconductor structures contact pad side tocontact pad side; d) etching through the photonic semiconductorstructure of between pixel regions to expose the device contact pads;and e) cutting the multi wafer into dies to form multiple emissivemulticolor digital image forming devices.
 3. The method of making a twodimensional array of multicolor light emitting pixels wherein each lightemitting pixel comprises a plurality of diode semiconductor structures,each for emitting a different color, stacked vertically with a grid ofvertical sidewalls electrically and optically separating each multicolorpixel from adjacent multicolor pixels within the array of multicolorpixels, and a plurality of vertical waveguides optically coupled to thediode semiconductor structures to vertically emit light generated by thediode semiconductor structures from a first surface of the stack ofsemiconductor structures; the method comprising: a) forming diodesemiconductor structures for emitting different colors, each havingmultiple semiconductor layers of one or more of the followingsemiconductors alloy materials: Al_(x)In_(1-x)P,(Al_(x)Ga_(1-x))_(y)In_(1-y)P, Ga_(x)In_(1-x)P, Al_(x)Ga_(1-x)N,Al_(x)Ga_(1-x)N/GaN, In_(x)Ga_(1-x)N, GaN, each formed on a separatewafer over a thick substrate layer of either GaAs, GaN or InGaN, eachincluding an n-type etch-stop layer and a p-type contact layer of thesame respective semiconductor substrate layer material type, eachcomprising n-type and p-type waveguide layers and cladding layers thatdefine their respective optical confinement regions, each having atleast one quantum well surrounded by two barrier layers that definetheir respective active regions, and each comprising an electron blockerlayer embedded either within their respective p-type waveguide layers orbetween their respective p-type waveguide and cladding layers; b)depositing a SiO₂ layer upon a Si-substrate wafer; c) depositing ann-contact metal layer over the SiO₂ layer; d) wafer-level bonding of thep-type contact layer of a diode semiconductor structure wafer of onecolor to the deposited n-contact metal layer and etching its GaAs, GaNor InGaN thick substrate down to its n-type etch-stop layer; e) etchinga grid of trenches with vertical sidewalls down to the n-contact metallayer and backfilling the etched trenches with SiO₂; f) etching thetrenches for vertical interconnect metal vias and backfilling etchedtrenches with metal; g) depositing a p-contact metal layer and etchingthe sidewall trenches; and h) depositing another SiO₂ layer; i)repeating b) through h) for each additional color of diode semiconductorstructure to be incorporated within the two dimensional array ofmulticolor light emitting pixels; j) depositing and etching a metallayer to form contact pads and refilling etched gaps with SiO₂; k)etching openings for the vertical waveguides though the Si-substrateside; l) depositing thin cladding layers on the interior walls ofopenings; and m) either backfilling the interior of the openingsremaining internal to the thin cladding layers with a dielectricmaterial or leaving them air filled.
 4. A method of making emissivemulticolor digital image founing devices comprising: a) founing a waferof two dimensional arrays of multicolor light emitting pixels wherebyeach multicolor light emitting pixel comprises a plurality of diodesemiconductor structures, each for emitting a different color, stackedvertically with a grid of vertical sidewalls electrically and opticallyseparating each multicolor pixel from adjacent multicolor pixels withinthe array of multicolor pixels, a plurality of vertical waveguidesoptically coupled to the diode semiconductor structures to verticallyemit light generated by the diode semiconductor structures from a firstsurface of the stack of diode semiconductor structures, and a pluralityof contact pads providing electrical contact to each diode semiconductorstructure; b) forming a wafer of digital semiconductor structures, eachhaving a plurality of digital semiconductor circuits in the respectivedigital semiconductor structure, each electrically coupled to receivecontrol signals from the periphery of the digital semiconductorstructure and electrically coupled to contact pads to separately controlon/off states of each of the multicolor diode semiconductor structuresthat may be connected thereto; c) wafer-level bonding the wafer of twodimensional arrays of multicolor light emitting pixels and the wafer ofdigital semiconductor structures contact pad side to contact pad side;d) etching through the photonic semiconductor structure between pixelregions to expose the device contact pads; and e) cutting the multiwafer into dies to form multiple emissive multicolor digital imageforming devices.